path: root/gprofng/doc/gprofng_ug.texi

\input texinfo @c -*-texinfo-*-

@c ----------------------------------------------------------------------------
@c This is the Texinfo source file for the GPROFNG manual.  This manual
@c includes the man pages for the various tools.
@c
@c Author: Ruud van der Pas
@c ----------------------------------------------------------------------------

@c %**start of header

@setfilename gprofng.info
@settitle GNU gprofng

@c -- Set the indent for the @example command to 1 space, not 5 ---------------
@exampleindent 1

@paragraphindent 3

@c %**end of header

@c -- Start a new chapter on a new, odd numbered, page ------------------------
@setchapternewpage odd

@c -- Merge all index entries into the Concepts Index -------------------------
@syncodeindex fn cp
@syncodeindex ky cp
@syncodeindex pg cp
@syncodeindex vr cp

@c -- Macros specific to gprofng ----------------------------------------------
@include gp-macros.texi

@c -- Get the version information ---------------------------------------------
@include version.texi

@c -- Entry for the Info dir structure ----------------------------------------
@ifnottex
@dircategory Software development
@direntry
* gprofng: (gprofng).                    The next generation profiling tool for Linux
@end direntry
@end ifnottex

@c -- Copyright stuff ---------------------------------------------------------
@copying
This document is the manual for @ProductName{}, last updated @value{UPDATED}.

Copyright @copyright{} 2022-2025 Free Software Foundation, Inc.

@c -- @quotation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License,
Version 1.3 or any later version published by the Free Software
Foundation; with no Invariant Sections, with no Front-Cover texts,
and with no Back-Cover Texts.  A copy of the license is included in the
section entitled ``GNU Free Documentation License.''

@c -- @end quotation
@end copying

@finalout
@smallbook

@c -- Define the title page ---------------------------------------------------
@titlepage
@title GNU gprofng
@subtitle The next generation profiling tool for Linux
@subtitle version @value{VERSION} (last updated @value{UPDATED})
@author Ruud van der Pas
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@c -- Generate the Table of Contents ------------------------------------------
@contents

@c -- The Top node ------------------------------------------------------------
@c Should contain a short summary, copying permissions and a master menu.
@c ----------------------------------------------------------------------------
@ifnottex
@node Top
@top  GNU Gprofng

@insertcopying
@end ifnottex

@ifinfo
@c -- The menu entries --------------------------------------------------------

@c * Display Source Code::             Display the source code and disassembly.
@c * Archive Experiment Data::         Archive an experiment.

@menu
* Introduction::                      About this manual.
* Overview::                          A brief overview of @ProductName{}.
* A Mini Tutorial::                   A short tutorial with the key features.
* The gprofng Tools::                 An overview of the tools supported.
* Performance Data Collection::       Record the performance information.
* View the Performance Information::  Different ways to view the data.
* Terminology::                       Concepts and terminology explained.
* Other Document Formats::            Create this document in other formats.
* The gprofng Man Pages::             The gprofng man pages.
* Index::                             The index.

@detailmenu

--- The Detailed Node Listing ---

Introduction

Overview

* Main Features::                     A high level overview.
* Sampling versus Tracing::           The pros and cons of both approaches.
* Steps Needed to Create a Profile::  How to create a profile.

A Mini Tutorial

* Getting Started::                 The basics of profiling with gprofng.
* Support for Multithreading::      Commands for multithreaded applications.
* View Multiple Experiments::       Analyze multiple experiments. 
* Profile Hardware Event Counters:: How to use hardware event counters.
* Java Profiling::                  How to profile a Java application.

The gprofng Tools

* Tools Overview::                            A brief description of the tools.
* The gprofng.rc file with default settings:: Customize the settings.
* Filters::                                   Filters.
* Supported Environment Variables::           The supported environment variables.

Performance Data Collection

* The @command{gprofng collect app} Tool::    Collect application performance data.

View the Performance Information

* The @command{gprofng display text} Tool::   View the performance data in plain text.

Terminology

* The Program Counter::                    What is a Program Counter?
* Inclusive and Exclusive Metrics::        An explanation of inclusive and exclusive metrics.
* Metric Definitions::                     Definitions associated with metrics.
* The Viewmode::                           Select the way call stacks are presented.
* The Selection List::                     How to define a selection.
* Load Objects and Functions::             The components in an application.
* The Concept of a CPU in gprofng::        The definition of a CPU.
* Hardware Event Counters Explained::      What are event counters?
* apath::                                  Our generic definition of a path.

The gprofng Man Pages

* Man page for @command{gprofng collect app}::   The man page for gprofng collect app.
* Man page for @command{gprofng display text}::  The man page for gprofng display text.
* Man page for @command{gprofng display html}::  The man page for gprofng display html.
* Man page for @command{gprofng display src}::   The man page for gprofng display src.
* Man page for @command{gprofng archive}::       The man page for gprofng archive.

@c -- Index

@end detailmenu
@end menu
@end ifinfo

@c -- A new node --------------------------------------------------------------
@node    Introduction
@chapter Introduction
@c ----------------------------------------------------------------------------
The @ProductName{} tool is the next generation profiler for Linux.  It consists
of various commands to generate and display profile information.

This manual starts with a tutorial how to create and interpret a profile.  This
part is highly practical and has the goal to get users up to speed as quickly
as possible.  As soon as possible, we would like to show you how to get your
first profile on your screen.

This is followed by more examples, covering many of the features.  At the
end of this tutorial, you should feel confident enough to tackle the more
complex tasks.

In a future update a more formal reference manual will be included as well.
Since even in this tutorial we use certain terminology, we have included a
chapter with descriptions at the end.  In case you encounter unfamiliar
wordings or terminology, please check this chapter.

One word of caution.  In several cases we had to somewhat tweak the screen
output in order to make it fit.  This is why the output may look somewhat
different when you try things yourself.

For now, we wish you a smooth profiling experience with @ProductName{} and
good luck tackling performance bottlenecks.

@c -- A new node --------------------------------------------------------------
@c cccccc @node    A Brief Overview of @ProductName{}
@node    Overview
@chapter A Brief Overview of gprofng
@c ----------------------------------------------------------------------------

@menu
* Main Features::                     A high level overview.
* Sampling versus Tracing::           The pros and cons of sampling versus tracing.
* Steps Needed to Create a Profile::  How to create a profile.
@end menu

Before we cover this tool in quite some detail, we start with a brief overview
of what it is, and the main features.  Since we know that many of you would
like to get started rightaway, already in this first chapter we explain the
basics of profiling with @ToolName{}.

@c ----------------------------------------------------------------------------
@c TBD Review this text.  Probably be more specific on the gcc releases and
@c processor specifics.
@c ----------------------------------------------------------------------------

@c -- A new node --------------------------------------------------------------
@node    Main Features
@section Main Features
@c ----------------------------------------------------------------------------

@noindent
These are the main features of the @ProductName{} tool:

@itemize @bullet

@item
Profiling is supported for an application written in C, C++, Java, or Scala.

@c TBD Java: up to 1.8 full support, support other than for modules

@item
Shared libraries are supported.  The information is presented at the
instruction level.

@item
The following multithreading programming models are supported: Pthreads,
OpenMP, and Java threads.

@item
This tool works with unmodified production level executables.  There is no need
to recompile the code, but if the @samp{-g} option has been used when building
the application, source line level information is available.

@item
The focus is on support for code generated with the @command{gcc} compiler, but
there is some limited support for the @command{icc} compiler as well.  Future
improvements and enhancements will focus on @command{gcc} though.

@item
Processors from Intel, AMD, and Arm are supported, but the level of support
depends on the architectural details.  In particular, hardware event counters
may not be supported.  If this is the case, all views not related to these
counters still ought to work though.

@item
Several views into the data are supported.  For example, a function overview
where the time is spent, but also a source line, disassembly, call tree and
a caller-callees overview are available.

@item
Through filters, the user can zoom in on an area of interest.

@item
Two or more profiles can be aggregated, or used in a comparison.  This
comparison can be obtained at the function, source line, and disassembly
level.

@item
Through a simple scripting language, and customization of the metrics shown,
the generation and creation of a profile can be fully automated and provide
tailored output.

@end itemize

@c -- A new node --------------------------------------------------------------
@node    Sampling versus Tracing
@section Sampling versus Tracing
@c ----------------------------------------------------------------------------

A key difference with some other profiling tools is that the main data
collection command @CollectApp{} mostly uses
@cindex Program Counter sampling
@cindex PC sampling
Program Counter (PC) sampling
under the hood.

With @emph{sampling}, the executable is interrupted at regular intervals.  Each
time it is halted, key information is gathered and stored.  This includes the
Program Counter that keeps track of where the execution is.  Hence the name.

Together with operational data, this information is stored in the experiment
directory and can be viewed in the second phase.

For example, the PC information is used to derive where the program was when
it was halted.  Since the sampling interval is known, it is relatively easy to
derive how much time was spent in the various parts of the program.

The opposite technique is generally referred to as @emph{tracing}.  With
tracing, the target is instrumented with specific calls that collect the
requested information.

These are some of the pros and cons of PC sampling verus tracing:

@itemize

@item
Since there is no need to recompile, existing executables can be used
and the profile measures the behaviour of exactly the same executable that is
used in production runs.

With sampling, one inherently profiles a different executable, because
the calls to the instrumentation library may affect the compiler optimizations
and run time behaviour.

@item
With sampling, there are very few restrictions on what can be profiled and
even without access to the source code, a basic profile can be made.

@item
A downside of sampling is that, depending on the sampling frequency, small
functions may be missed or not captured accurately.  Although this is rare,
this may happen and is the reason why the user has control over the sampling
rate.

@item
While tracing produces precise information, sampling is statistical in nature.
As a result, small variations may occur across seemingly identical runs.  We
have not observed more than a few percent deviation though.  Especially if
the target job executed for a sufficiently long time.

@item
With sampling, it is not possible to get an accurate count how often
functions are called.

@end itemize

@c -- A new node --------------------------------------------------------------
@node    Steps Needed to Create a Profile
@section Steps Needed to Create a Profile
@c ----------------------------------------------------------------------------

Creating a profile takes two steps.  First the profile data needs to be
generated.  This is followed by a viewing step to create a report from the
information that has been gathered.

Every @ProductName{} command starts with @ToolName{}, the name of the driver.
This is followed by a keyword to define the high level functionality.
Depending on this keyword, a third qualifier may be needed to further narrow
down the request.
This combination is then followed by options that are specific to the
functionality desired.

The command to gather, or ``collect'', the performance data is called
@CollectApp{}.  Aside from numerous options, this command takes the name
of the target executable as an input parameter.

Upon completion of the run, the performance data can be
found in the newly created
@cindex Experiment directory
experiment directory.

Unless explicitly specified otherwise, a default
name for this directory is chosen.  The name is @file{test.<n>.er} where
@var{<n>} is the first integer number not in use yet for such a name.

For example, the first time @CollectApp{} is invoked, an experiment
directory with the name @file{test.1.er} is created.
Upon a subsequent invocation of @CollectApp{} in the same directory,
an experiment directory with the name @file{test.2.er} will be created,
and so forth.

Note that @CollectApp{} supports an option to explicitly name the experiment
directory.
Aside from the restriction that the name of this directory has to end
with @samp{.er}, any valid directory name can be used for this.

Now that we have the performance data, the next step is to display it.

@IndexSubentry{@code{gprofng}, @code{display text}}
The most commonly used command to view the performance information is
@DisplayText{}.   This is a very extensive and customizable tool that
produces the information in ASCII format.

@IndexSubentry{@code{gprofng}, @code{display html}}
Another option is to use @DisplayHTML{}.  This tool generates a directory with
files in html format.  These can be viewed in a browser, allowing for easy
navigation through the profile data.

@c -- A new node --------------------------------------------------------------
@node    A Mini Tutorial
@chapter A Mini Tutorial
@c ----------------------------------------------------------------------------

In this chapter we present and discuss the main functionality of @ToolName{}.
This will be a practical approach, using an example code to generate profile
data and show how to get various performance reports.

@menu
* Getting Started::                 The basics of profiling with @ProductName().
* Support for Multithreading::      Commands specific to multithreaded applications.
* View Multiple Experiments::       Analyze multiple experiments simultaneously.
* Profile Hardware Event Counters:: How to use hardware event counters.
* Java Profiling::                  How to profile a Java application.
@end menu

@c -- A new node --------------------------------------------------------------
@node    Getting Started
@section Getting Started
@c ----------------------------------------------------------------------------

The information presented here provides a good and common basis for many
profiling tasks, but there are more features that you may want to leverage.

These are covered in subsequent sections in this chapter.

@menu
* The Example Program::                        A description of the example program used.
* A First Profile::                            How to get the first profile.
* The Source Code View::                       Display the metrics in the source code.
* The Disassembly View::                       Display the metrics at the instruction level.
* Display and Define the Metrics::             An example how to customize the metrics.
* Customization of the Output::                An example how to customize the output.
* Name the Experiment Directory::              Change the name of the experiment directory.
* Control the Number of Lines in the Output::  Change the number of lines in the tables.
* Sorting the Performance Data::               How to set the metric to sort by.
* Scripting::                                  Use a script to execute the commands.
* A More Elaborate Example::                   An example of customization.
* The Call Tree::                              Display the dynamic call tree.
* More Information on the Experiment::         How to get additional statistics.
* Control the Sampling Frequency::             How to control the sampling granularity.
* Information on Load Objects::                How to get more information on load objects.
@end menu

@c -- A new node --------------------------------------------------------------
@node       The Example Program
@subsection The Example Program
@c ----------------------------------------------------------------------------

Throughout this guide we use the same example C code that implements the
multiplication of a vector of length @math{n} by an @math{m} by @math{n}
matrix.  The result is stored in a vector of length @math{m}.
@cindex Pthreads
@cindex Posix Threads
The algorithm has been parallelized using Posix Threads, or Pthreads for short.

The code was built using the @code{gcc} compiler and the name of the executable
is
@cindex mxv-pthreads
@command{mxv-pthreads}.

The matrix sizes can be set through the @code{-m} and @code{-n} options.  The
number of threads is set with the @code{-t} option.  These are additional
threads that are used in the multiplication.  To increase the duration of
the run, the computations are executed repeatedly.

This is an example that multiplies a @math{8000} by @math{4000} matrix with
a vector of length @math{4000}.  Although this is a multithreaded application,
initially we will be using @math{1} threads.  Later on we will show examples
using multiple threads.

@smallexample
@verbatim
$ ./mxv-pthreads -m 8000 -n 4000 -t 1
mxv: error check passed - rows = 8000 columns = 4000 threads = 1
$
@end verbatim
@end smallexample

The program performs an internal check to verify that the computed results
are correct.  The result of this check is printed, as well as the matrix
sizes and the number of threads used.

@c -- A new node --------------------------------------------------------------
@node       A First Profile
@subsection A First Profile
@c ----------------------------------------------------------------------------

The first step is to collect the performance data.  It is important to remember
that much more information is gathered than may be shown by default.  Often a
single data collection run is sufficient to get a lot of insight.

The @CollectApp{} command is used for the data collection.  Nothing needs to be
changed in the way the application is executed.  The only difference is that it
is now run under control of the tool, as shown below:

@cartouche
@smallexample
$ gprofng collect app ./mxv-pthreads -m 8000 -n 4000 -t 1
@end smallexample
@end cartouche

@noindent
This produces the following output:

@smallexample
@verbatim
Creating experiment directory test.1.er (Process ID: 2749878) ...
mxv: error check passed - rows = 8000 columns = 4000 threads = 1
@end verbatim
@end smallexample

We see a message that an experiment directory with the name @file{test.1.er}
has been created.  The process id is also echoed.  The application completes
as usual and we have our first experiment directory that can be analyzed.

The tool we use for this is called @DisplayText{}.  It takes the name of
the experiment directory as an argument.

@cindex Interpreter mode
If invoked this way, the tool starts in the interactive @emph{interpreter}
mode.
While in this environment, commands can be given and the tool responds.  This
is illustrated below:

@smallexample
@verbatim
$ gprofng display text test.1.er
Warning: History and command editing is not supported on this system.
(gprofng-display-text) quit
$
@end verbatim
@end smallexample

@cindex Command line mode
While useful in certain cases, we prefer to use this tool in command line mode
by specifying the commands to be issued when invoking the tool.  The way to do
this is to prepend the command(s) with a hyphen (@samp{-}) if used on the
command line.

Since this makes the command appear to be an option, they are also sometimes
referred to as such, but technically they are commands.  This is the
terminology we will use in this user guide, but for convenience the commands
are also listed as options in the index.

For example,
@IndexSubentry{Options,  @code{-functions}}
@IndexSubentry{Commands, @code{functions}}
below we use the @command{functions} command to request a list of the functions
that have been executed, plus their respective CPU times:

@cartouche
@smallexample
$ gprofng display text -functions test.1.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total   Incl. Total    Name
CPU           CPU
 sec.      %   sec.      %
9.367 100.00  9.367 100.00   <Total>
8.926  95.30  8.926  95.30   mxv_core
0.210   2.24  0.420   4.49   init_data
0.080   0.85  0.210   2.24   drand48
0.070   0.75  0.130   1.39   erand48_r
0.060   0.64  0.060   0.64   __drand48_iterate
0.010   0.11  0.020   0.21   _int_malloc
0.010   0.11  0.010   0.11   sysmalloc
0.      0.    8.926  95.30   <static>@0x47960 (<libgp-collector.so>)
0.      0.    0.440   4.70   __libc_start_main
0.      0.    0.020   0.21   allocate_data
0.      0.    8.926  95.30   driver_mxv
0.      0.    0.440   4.70   main
0.      0.    0.020   0.21   malloc
0.      0.    8.926  95.30   start_thread
@end verbatim
@end smallexample

@noindent
As easy and simple as these steps are, we do have a first profile of our
program!

There are five columns.  The first four contain the
@cindex Total CPU time
''Total CPU Time'', which
is the sum of the user and system time. @xref{Inclusive and Exclusive Metrics}
for an explanation of ``exclusive'' and ``inclusive'' times.

The first line echoes the metric that is used to sort the output.  By default,
this is the exclusive CPU time, but through the @command{sort} command, the
sort metric can be changed by the user.

Next, there are four columns with the exclusive and inclusive CPU times and the
respective percentages.  This is followed by the name of the function.

@IndexSubentry{Miscellaneous, @code{<Total>}}
The function with the name @code{<Total>} is not a user function.  It is a
pseudo function introduced by @ToolName{}.  It is used to display the
accumulated measured metric values.  In this example, we see that the total
CPU time of this job was 9.367 seconds and it is scaled to 100%.  All
other percentages in the same column are relative to this number.

@c -- If the metric is derived, for example the @code{IPC}, the value shown
@c -- under
@c -- @code{<Total>} is based upon the total values of the that are metrics
@c -- used to
@c -- compute the derived metric.
@c -- @IndexSubentry{Hardware event counters, IPC}

With 8.926 seconds, function @code{mxv_core} takes 95.30% of the
total time and is by far the most time consuming function.
The exclusive and inclusive metrics are identical, which means that it
is a leaf function not calling any other functions.

The next function in the list is @code{init_data}.  Although with 4.49%,
the CPU time spent in this part is modest, this is an interesting entry because
the inclusive CPU time of 0.420 seconds is twice the exclusive CPU time
of 0.210 seconds.  Clearly this function is calling another function,
or even more than one function and collectively this takes 0.210 seconds.
Below we show the call tree feature that provides more details on the call
structure of the application.

The function @code{<static>@@0x47960 (<libgp-collector.so>)} does odd and
certainly not familiar.  It is one of the internal functions used by
@CollectApp{} and can be ignored.  Also, while the inclusive time is high,
the exclusive time is zero.  This means it doesn't contribute to the
performance.

The question is how we know where this function originates from.  There are
several commands to dig deeper an get more details on a function.
@xref{Information on Load Objects}.

@c -- A new node --------------------------------------------------------------
@node       The Source Code View
@subsection The Source Code View
@c ----------------------------------------------------------------------------

In general, the tuning efforts are best focused on the most time consuming
part(s) of an application.  In this case that is easy, since over 95% of
the total CPU time is spent in function @code{mxv_core}.
It is now time to dig deeper and look
@cindex Source level metrics
at the metrics distribution at the source code level.  Since we measured
CPU times, these are the metrics shown.

@IndexSubentry{Options,  @code{-source}}
@IndexSubentry{Commands, @code{source}}
The @code{source} command is used to accomplish this.  It takes the name of the
function, not the source filename, as an argument.  This is demonstrated
below, where the @DisplayText{} command is used to show the annotated
source listing of function @code{mxv_core}.

Be aware that when using the @command{gcc} compiler, the source code has to
be compiled with the @code{-g} option in order for the source code feature
to work.  Otherwise the location(s) can not be determined.  For other compilers
we recommend to check the documentation for such an option.

Below the command to display the source code of a function is shown.  Since at
this point we are primarily interested in the timings only, we use the
@code{metrics} command to request the exclusive and inclusive total CPU
timings only. @xref{Display and Define the Metrics} for more information
how to define the metrics to be displayed.

@cartouche
@smallexample
$ gprofng display text -metrics ei.totalcpu -source mxv_core test.1.er
@end smallexample
@end cartouche

The output is shown below.  It has been somewhat modified to fit the formatting
constraints and reduce the number of lines.

@smallexample
@verbatim
Current metrics: e.totalcpu:i.totalcpu:name
Current Sort Metric: Exclusive Total CPU Time ( e.totalcpu )
Source file: <apath>/mxv.c
Object file: mxv-pthreads (found as test.1.er/archives/...)
Load Object: mxv-pthreads (found as test.1.er/archives/...)

   Excl.     Incl.
   Total     Total
   CPU sec.  CPU sec.

   <lines deleted>
                                <Function: mxv_core>
                            43. void __attribute__ ((noinline)) 
                                     mxv_core (int64_t row_index_start,
                            44.                int64_t row_index_end,
                            45.                int64_t m,
                            46.                int64_t n,
                            47.                double **restrict A,
                            48.                double *restrict b,
                            49.                double *restrict c)
                            50. {
   0.        0.             50. {
   0.        0.             51.   for (int64_t i=row_index_start;
                                                 i<=row_index_end; i++)
                            52.     {
   0.        0.             53.       double row_sum = 0.0;
## 4.613     4.613          54.       for (int64_t j=0; j<n; j++)
## 4.313     4.313          55.         row_sum += A[i][j] * b[j];
   0.        0.             56.       c[i] = row_sum;
                            57.     }
   0.        0.             58. }
@end verbatim
@end smallexample

The first line echoes the metrics that have been selected.  The second line
is not very meaningful when looking at the source code listing, but it shows
the metric that is used to sort the data.

The next three lines provide information on the location of the source file,
the object file and the load object (@xref{Load Objects and Functions}).

Function @code{mxv_core} is part of a source file that has other functions
as well.  These functions will be shown with the values for the metrics, but
for lay-out purposes they have been removed in the output shown above.

The header is followed by the annotated source code listing.  The selected
metrics are shown first, followed by a source line number, and the source code.
@IndexSubentry{Miscellaneous ,@code{##}}
The most time consuming line(s) are marked with the @code{##} symbol.  In
this way they are easier to identify and find with a search.

What we see is that all of the time is spent in lines 54-55.

@IndexSubentry{Options,  @code{-lines}}
@IndexSubentry{Commands, @code{lines}}
A related command sometimes comes handy as well.  It is called @code{lines}
and displays a list of the source lines and their metrics, ordered according
to the current sort metric (@xref{Sorting the Performance Data}).

Below the command and the output.  For lay-out reasons, only the top 10 is
shown here and the last part of the text on some lines has been replaced
by dots.  The full text is @samp{instructions without line numbers} and
means that the line number information for that function was not found.

@cartouche
@smallexample
$ gprofng display text -lines test.1.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Lines sorted by metric: Exclusive Total CPU Time

Excl. Total   Incl. Total    Name
CPU           CPU
 sec.      %   sec.      %
9.367 100.00  9.367 100.00   <Total>
4.613  49.25  4.613  49.25   mxv_core, line 54 in "mxv.c"
4.313  46.05  4.313  46.05   mxv_core, line 55 in "mxv.c"
0.160   1.71  0.370   3.95   init_data, line 118 in "manage_data.c"
0.080   0.85  0.210   2.24   <Function: drand48, instructions ...>
0.070   0.75  0.130   1.39   <Function: erand48_r, instructions ...>
0.060   0.64  0.060   0.64   <Function: __drand48_iterate, ...>
0.040   0.43  0.040   0.43   init_data, line 124 in "manage_data.c"
0.010   0.11  0.020   0.21   <Function: _int_malloc, instructions ...>
0.010   0.11  0.010   0.11   <Function: sysmalloc, instructions ...>
@end verbatim
@end smallexample

What this overview immediately highlights is that the third most time consuming
source line takes 0.370 seconds only.  This means that the inclusive time is
only 3.95% and clearly this branch of the code hardly impacts the performance.

@c -- A new node --------------------------------------------------------------
@node       The Disassembly View
@subsection The Disassembly View
@c ----------------------------------------------------------------------------

The source view is very useful to obtain more insight where the time is spent,
but sometimes this is not sufficient.  The disassembly view provides more
details since it shows the metrics at the instruction level.

This view is displayed with the
@IndexSubentry{Options,  @code{-disasm}}
@IndexSubentry{Commands, @code{disasm}}
@command{disasm}
command and as with the source view, it displays an annotated listing.  In this
@cindex Instruction level metrics
case it shows the instructions with the metrics, interleaved with the
source lines.  The
instructions have a reference in square brackets (@code{[} and @code{]})
to the source line they correspond to.

@noindent
We again focus on the tmings only and set the metrics accordingly:

@cartouche
@smallexample
$ gprofng display text -metrics ei.totalcpu -disasm mxv_core test.1.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Current metrics: e.totalcpu:i.totalcpu:name
Current Sort Metric: Exclusive Total CPU Time ( e.totalcpu )
Source file: <apath>/src/mxv.c
Object file: mxv-pthreads (found as test.1.er/archives/...)
Load Object: mxv-pthreads (found as test.1.er/archives/...)

   Excl.     Incl.
   Total     Total
   CPU sec.  CPU sec.

   <lines deleted>
                      43. void __attribute__ ((noinline)) 
                               mxv_core (int64_t row_index_start,
                      44.                int64_t row_index_end,
                      45.                int64_t m,
                      46.                int64_t n,
                      47.                double **restrict A,
                      48.                double *restrict b,
                      49.                double *restrict c)
                      50. {
                          <Function: mxv_core>
   0.        0.           [50]   401d56:  mov    0x8(%rsp),%r10
                      51.   for (int64_t i=row_index_start;
                                           i<=row_index_end; i++)
   0.        0.           [51]   401d5b:  cmp    %rsi,%rdi
   0.        0.           [51]   401d5e:  jg     0x47
   0.        0.           [51]   401d60:  add    $0x1,%rsi
   0.        0.           [51]   401d64:  jmp    0x36
                      52.     {
                      53.       double row_sum = 0.0;
                      54.       for (int64_t j=0; j<n; j++)
                      55          row_sum += A[i][j] * b[j];
   0.        0.           [55]   401d66:  mov    (%r8,%rdi,8),%rdx
   0.        0.           [54]   401d6a:  mov    $0x0,%eax
   0.        0.           [53]   401d6f:  pxor   %xmm1,%xmm1
   0.110     0.110        [55]   401d73:  movsd  (%rdx,%rax,8),%xmm0
   1.921     1.921        [55]   401d78:  mulsd  (%r9,%rax,8),%xmm0
   2.282     2.282        [55]   401d7e:  addsd  %xmm0,%xmm1
## 4.613     4.613        [54]   401d82:  add    $0x1,%rax
   0.        0.           [54]   401d86:  cmp    %rax,%rcx
   0.        0.           [54]   401d89:  jne    0xffffffffffffffea
                      56.       c[i] = row_sum;
   0.        0.           [56]   401d8b:  movsd  %xmm1,(%r10,%rdi,8)
   0.        0.           [51]   401d91:  add    $0x1,%rdi
   0.        0.           [51]   401d95:  cmp    %rsi,%rdi
   0.        0.           [51]   401d98:  je     0xd
   0.        0.           [53]   401d9a:  pxor   %xmm1,%xmm1
   0.        0.           [54]   401d9e:  test   %rcx,%rcx
   0.        0.           [54]   401da1:  jg     0xffffffffffffffc5
   0.        0.           [54]   401da3:  jmp    0xffffffffffffffe8
                      57.     }
                      58. }
   0.        0.           [58]   401da5:  ret
@end verbatim
@end smallexample

For each instruction, the timing values are given and we can immediately
identify the most expensive instructions.  As with the source level view,
these are marked with the @code{##} symbol.

It comes as no surprise that the time consuming instructions originate from
the source code at lines 54-55.
One thing to note is that the source line numbers no longer appear in
sequential order.
This is because the compiler has re-ordered the instructions as part of
the code optimizations it has performed.

As illustrated below and similar to the @command{lines} command, we can get
an overview of the instructions executed by using the
@IndexSubentry{Options,  @code{-pcs}}
@IndexSubentry{Commands, @code{pcs}}
@command{pcs}
command.

@noindent
Below the command and the output, which again has been restricted
to 10 lines.  As before, some lines have been shortened for lay-out
purposes.

@cartouche
@smallexample
$ gprofng display text -pcs test.1.er
@end smallexample
@end cartouche

@smallexample
@verbatim
PCs sorted by metric: Exclusive Total CPU Time

Excl. Total   Incl. Total    Name
CPU           CPU
 sec.      %   sec.      %
9.367 100.00  9.367 100.00   <Total>
4.613  49.25  4.613  49.25   mxv_core + 0x0000002C, line 54 in "mxv.c"
2.282  24.36  2.282  24.36   mxv_core + 0x00000028, line 55 in "mxv.c"
1.921  20.51  1.921  20.51   mxv_core + 0x00000022, line 55 in "mxv.c"
0.150   1.60  0.150   1.60   init_data + 0x000000AC, line 118 in ...
0.110   1.18  0.110   1.18   mxv_core + 0x0000001D, line 55 in "mxv.c"
0.040   0.43  0.040   0.43   drand48 + 0x00000022
0.040   0.43  0.040   0.43   init_data + 0x000000F1, line 124 in ...
0.030   0.32  0.030   0.32   __drand48_iterate + 0x0000001E
0.020   0.21  0.020   0.21   __drand48_iterate + 0x00000038
@end verbatim
@end smallexample

@noindent
What we see is that the top three instructions take 94% of the total CPU time
and any optimizations should focus on this part of the code..

@c -- A new node --------------------------------------------------------------
@node       Display and Define the Metrics
@subsection Display and Define the Metrics
@c ----------------------------------------------------------------------------

The metrics shown by @DisplayText{} are useful, but there is more recorded
than displayed by default.  We can customize the values shown by defining the
metrics ourselves.

There are two commands related to changing the metrics shown:
@IndexSubentry{Options,  @code{-metric_list}}
@IndexSubentry{Commands, @code{metric_list}}
@command{metric_list} and
@IndexSubentry{Options,  @code{-metrics}}
@IndexSubentry{Commands, @code{metrics}}
@command{metrics}.

The first command shows the currently selected metrics, plus all the metrics
that have been stored as part of the experiment.  The second command may be
used to define the metric list.

@noindent
This is the way to get the information about the metrics:

@IndexSubentry{Options,  @code{-metric_list}}
@IndexSubentry{Commands, @code{metric_list}}
@cartouche
@smallexample
$ gprofng display text -metric_list test.1.er
@end smallexample
@end cartouche

@noindent
This is the output:

@smallexample
@verbatim
Current metrics: e.%totalcpu:i.%totalcpu:name
Current Sort Metric: Exclusive Total CPU Time ( e.%totalcpu )
Available metrics:
Exclusive Total CPU Time: e.%totalcpu
Inclusive Total CPU Time: i.%totalcpu
                    Size: size
              PC Address: address
                    Name: name
@end verbatim
@end smallexample

This shows the metrics that are currently used, the metric that is used to sort
the data and all the metrics that have been recorded, but are not necessarily
shown.

@cindex Default metrics
In this case, the current metrics are set to the exclusive and inclusive
total CPU times, the respective percentages, and the name of the function,
or load object.

@IndexSubentry{Options,  @code{-metrics}}
@IndexSubentry{Commands, @code{metrics}}
The @code{metrics} command is used to define the metrics that need to be
displayed.

For example, to swap the exclusive and inclusive metrics, use the following
metric definition: @code{i.%totalcpu:e.%totalcpu}.

Since the metrics can be tailored for different views, there is also a way
to reset them to the default.  This is done through the special keyword
@code{default} for the metrics definition (@command{-metrics default}).
@IndexSubentry{Metrics, Reset to default}

@c -- A new node --------------------------------------------------------------
@node       Customization of the Output
@subsection Customization of the Output
@c ----------------------------------------------------------------------------

With the information just given, the function overview can be customized.
For sake of the example, we would like to display the name of the function
first, only followed by the exclusive CPU time, given as an absolute number
and a percentage.

Note that the commands are parsed in order of appearance.  This is why we
need to define the metrics @emph{before} requesting the function overview:

@cartouche
@smallexample
$ gprofng display text -metrics name:e.%totalcpu -functions test.1.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Current metrics: name:e.%totalcpu
Current Sort Metric: Exclusive Total CPU Time ( e.%totalcpu )
Functions sorted by metric: Exclusive Total CPU Time

Name                                     Excl. Total
                                         CPU
                                          sec.      %
 <Total>                                 9.367 100.00
 mxv_core                                8.926  95.30
 init_data                               0.210   2.24
 drand48                                 0.080   0.85
 erand48_r                               0.070   0.75
 __drand48_iterate                       0.060   0.64
 _int_malloc                             0.010   0.11
 sysmalloc                               0.010   0.11
 <static>@0x47960 (<libgp-collector.so>) 0.      0.
 __libc_start_main                       0.      0.
 allocate_data                           0.      0.
 driver_mxv                              0.      0.
 main                                    0.      0.
 malloc                                  0.      0.
 start_thread                            0.      0.
@end verbatim
@end smallexample

This was a first and simple example how to customize the output.  Note that we
did not rerun our profiling job and merely modified the display settings.
Below we will show other and also more advanced examples of customization.

@c -- A new node --------------------------------------------------------------
@node       Name the Experiment Directory
@subsection Name the Experiment Directory
@c ----------------------------------------------------------------------------

When using @CollectApp{}, the default names for experiments work fine, but
they are quite generic.  It is often more convenient to select a more
descriptive name.  For example, one that reflects conditions for the experiment
conducted, like the number of threads used.

For this, the mutually exclusive @code{-o} and @code{-O} options come in handy.
Both may be used to provide a name for the experiment directory, but the
behaviour of @CollectApp{} is different.

With the
@IndexSubentry{Options, @code{-o}}
@samp{-o}
option, an existing experiment directory is not overwritten.  Any directory
with the same name either needs to be renamed, moved, or removed, before the
experiment can be conducted.

This is in contrast with the behaviour for the
@IndexSubentry{Options, @code{-O}}
@samp{-O}
option.  Any existing directory with the same name is silently overwritten.

Be aware that the name of the experiment directory has to end with @file{.er}.

@c -- A new node --------------------------------------------------------------
@node       Control the Number of Lines in the Output
@subsection Control the Number of Lines in the Output
@c ----------------------------------------------------------------------------

@IndexSubentry{Options,  @code{-limit}}
@IndexSubentry{Commands, @code{limit}}
The @command{limit} @var{<n>} command can be used to control the number of
lines printed in various views.  For example it impacts the function view, but
also takes effect for other display commands, like @command{lines}.

The argument @var{<n>} should be a positive integer number.  It sets the number
of lines in the (function) view.  A value of zero resets the limit to the
default.

Be aware that the pseudo-function @code{<Total>} counts as a regular function.
For example @command{limit 10} displays nine user level functions.

@c -- A new node --------------------------------------------------------------
@node       Sorting the Performance Data
@subsection Sorting the Performance Data
@c ----------------------------------------------------------------------------

@IndexSubentry{Options,  @code{-sort}}
@IndexSubentry{Commands, @code{sort}}
The @command{sort} @var{<key>} command sets the key to be used when sorting the
performance data.

The key is a valid metric definition, but the
@IndexSubentry{Metrics, Visibility field}
visibility field
(@xref{Metric Definitions})
in the metric
definition is ignored, since this does not affect the outcome of the sorting
operation.
For example if the sort key is set to @code{e.totalcpu}, the values
will be sorted in descending order with respect to the exclusive total
CPU time.

@IndexSubentry{Sort, Reverse order}
The data can be sorted in reverse order by prepending the metric definition
with a minus (@samp{-}) sign.  For example @command{sort -e.totalcpu}.

@IndexSubentry{Sort, Reset to default}
A default metric for the sort operation has been defined and since this is
a persistent command, this default can be restored with @code{default} as
the key (@command{sort default}).

@c -- A new node --------------------------------------------------------------
@node       Scripting
@subsection Scripting
@c ----------------------------------------------------------------------------

@cindex Script files
The list with commands for @DisplayText{} can be very long.  This is tedious
and also error prone.  Luckily, there is an easier and elegant way to control
the output of this tool.

@IndexSubentry{Options,  @code{-script}}
@IndexSubentry{Commands, @code{script}}
Through the @command{script} command, the name of a file with commands can be
passed in.  These commands are parsed and executed as if they appeared on
the command line in the same order as encountered in the file.  The commands
in this script file can actually be mixed with commands on the command line
and multiple script files may be used.
The difference between the commands in the script file and those used on the
command line is that the latter require a leading dash (@samp{-}) symbol.

Comment lines in a script file are supported.  They need to start with the
@samp{#} symbol.

@c -- A new node --------------------------------------------------------------
@node       A More Elaborate Example
@subsection A More Elaborate Example
@c ----------------------------------------------------------------------------

With the information presented so far, we can customize our data
gathering and display commands.

As an example, we would like to use @file{mxv.1.thr.er} as the name for the
experiment directory.  In this way, the name of the algorithm and the
number of threads that were used are included in the name.
We also don't mind to overwrite an existing
experiment directory with the same name.

All that needs to be done is to use the
@IndexSubentry{Options, @code{-O}}
@samp{-O}
option, followed by the directory name of choice when running @CollectApp{}:

@cartouche
@smallexample
$ exe=mxv-pthreads
$ m=8000
$ n=4000
$ gprofng collect app -O mxv.1.thr.er ./$exe -m $m -n $n -t 1
@end smallexample
@end cartouche

Since we want to customize the profile and prefer to keep the command line
short, the commands to generate the profile are put into a file with the
name @file{my-script}:

@smallexample
@verbatim
$ cat my-script
# This is my first gprofng script
# Set the metrics
metrics i.%totalcpu:e.%totalcpu:name
# Use the exclusive time to sort
sort e.totalcpu
# Limit the function list to 5 lines
limit 5
# Show the function list
functions
@end verbatim
@end smallexample

This script file is specified as input to the @DisplayText{} command
that is used to display the performance information stored in experiment
directory @file{mxv.1.thr.er}:

@cartouche
@smallexample
$ gprofng display text -script my-script mxv.1.thr.er
@end smallexample
@end cartouche

This command produces the following output:

@smallexample
@verbatim
# This is my first gprofng script
# Set the metrics
Current metrics: i.%totalcpu:e.%totalcpu:name
Current Sort Metric: Exclusive Total CPU Time ( e.%totalcpu )
# Use the exclusive time to sort
Current Sort Metric: Exclusive Total CPU Time ( e.%totalcpu )
# Limit the function list to 5 lines
Print limit set to 5
# Show the function list
Functions sorted by metric: Exclusive Total CPU Time

Incl. Total   Excl. Total    Name
CPU           CPU
 sec.      %   sec.      %
9.703 100.00  9.703 100.00   <Total>
9.226  95.09  9.226  95.09   mxv_core
0.455   4.69  0.210   2.17   init_data
0.169   1.75  0.123   1.26   erand48_r
0.244   2.52  0.075   0.77   drand48
@end verbatim
@end smallexample

In the first part of the output the comment lines in the script file are
echoed.  These are interleaved with an acknowledgement message for the
commands.

This is followed by a profile consisting of 5 lines only.  For both metrics,
the percentages plus the timings are given.  The numbers are sorted with
respect to the exclusive total CPU time.  Although this is the default, for
demonstration purposes we use the @command{sort} command to explicitly define
the metric for the sort.

While we executed the same job as before and only changed the name of the
experiment directory, the results are somewhat different.  This is sampling
in action.  The numbers are not all that different though.
It is seen that function @code{mxv_core} is responsbile for
95% of the CPU time and @code{init_data} takes 4.5% only.

@c -- A new node --------------------------------------------------------------
@node       The Call Tree
@subsection The Call Tree
@c ----------------------------------------------------------------------------

The call tree shows the dynamic structure of the application by displaying the
functions executed and their parent.  The CPU time attributed to each function
is shown as well.  This view helps to find the most expensive
execution path in the program.

@IndexSubentry{Options,  @code{-calltree}}
@IndexSubentry{Commands, @code{calltree}}
This feature is enabled through the @command{calltree} command.  For example,
this is how to get the call tree for our current experiment:

@cartouche
@smallexample
$ gprofng display text -calltree mxv.1.thr.er
@end smallexample
@end cartouche

This displays the following structure:

@smallexample
@verbatim
Functions Call Tree. Metric: Attributed Total CPU Time

Attr. Total    Name
CPU
 sec.      %
9.703 100.00   +-<Total>
9.226  95.09     +-start_thread
9.226  95.09     |  +-<static>@0x47960 (<libgp-collector.so>)
9.226  95.09     |    +-driver_mxv
9.226  95.09     |      +-mxv_core
0.477   4.91     +-__libc_start_main
0.477   4.91       +-main
0.455   4.69         +-init_data
0.244   2.52         |  +-drand48
0.169   1.75         |    +-erand48_r
0.047   0.48         |      +-__drand48_iterate
0.021   0.22         +-allocate_data
0.021   0.22         |  +-malloc
0.021   0.22         |    +-_int_malloc
0.006   0.06         |      +-sysmalloc
0.003   0.03         |        +-__default_morecore
0.003   0.03         |          +-sbrk
0.003   0.03         |            +-brk
0.001   0.01         +-pthread_create
0.001   0.01           +-__pthread_create_2_1
@end verbatim
@end smallexample

At first sight this may not be what is expected and some explanation is in
place.

@c ----------------------------------------------------------------------------
@c TBD: Revise this text when we have user and machine mode.
@c ----------------------------------------------------------------------------
The top function is the pseudo-function @code{<Total>} that we have seen
before.  It is introduced and shown here to provide the total value of the
metric(s).

We also see function @code{<static>@@0x47960} in the call tree and apparently
it is from @code{libgp-collector.so}, a library that is internal to
@ToolName{}.
The @code{<static>} marker, followed by the program counter, is shown if the
name of the function cannot be found.  This function is part of the
implementation of the data collection process and should be hidden to the
user.  This is part of a planned future enhancement.

In general, if a view has a function that does not appear to be part of the
user code, or seems odd anyhow, the @command{objects} and @command{fsingle}
@IndexSubentry{Options,  @code{-objects}}
@IndexSubentry{Commands, @code{objects}}
@IndexSubentry{Options,  @code{-fsingle}}
@IndexSubentry{Commands, @code{fsingle}}
commands are very useful
to find out more about load objects in general, but also to help identify
an unknown entry in the function overview. @xref{Load Objects and Functions}.

Another thing to note is that there are two main branches.  The one under
@code{<static>@@0x47960} and the second one under @code{__libc_start_main}.
This reflects the fact that this is a multithreaded program and the
threaded part shows up as a separate branch in the call tree.

The way to interpret this structure is as follows.  The program starts
under control of @code{__libc_start_main}.  This executes the main program
called @code{main}, which at the top level executes functions
@code{init_data}, @code{allocate_data}, and @code{pthread_create}.
The latter function creates and executes the additional thread(s).

For this multithreaded part of the code, we need to look at the branch
under function @code{start_thread} that calls the driver code for the
matrix-vector multiplication (@code{driver_mxv}), which executes the function
that performs the actual multiplication (@code{mxv_core}).

There are two things worth noting for the call tree feature:

@itemize

@item
This is a dynamic tree and since sampling is used, it most likely looks
slighlty different across seemingly identical profile runs.  In case the
run times are short, it is worth considering to use a high resolution
through the
@IndexSubentry{Options, @code{-p}}
@samp{-p}
option.  For example use @samp{-p hi} to increase the sampling rate.

@item
In case hardware event counters have been enabled
(@xref{Profile Hardware Event Counters}), these values are also displayed
in the call tree view.

@end itemize

@c -- A new node --------------------------------------------------------------
@node       More Information on the Experiment
@subsection More Information on the Experiment
@c ----------------------------------------------------------------------------

The experiment directory not only contains performance related data.  Several
system characteristics, the profiling command executed, plus some global
performance statistics are stored and can be displayed.

@IndexSubentry{Options,  @code{-header}}
@IndexSubentry{Commands, @code{header}}
The @command{header} command displays information about the experiment(s).
For example, this is command is used to extract this data from for our
experiment directory:

@cartouche
@smallexample
$ gprofng display text -header mxv.1.thr.er
@end smallexample
@end cartouche

The above command prints the following information.  Note that some of the
lay-out and the information has been modified.  Directory paths have been
replaced @code{<apath>} for example.  Textual changes are
marked with the @samp{<} and @samp{>} symbols.

@smallexample
@verbatim
Experiment: mxv.1.thr.er
No errors
No warnings
Archive command ` /usr/bin/gprofng-archive -n -a on --outfile
                     <apath>/archive.log <apath>/mxv.1.thr.er'

Target command (64-bit): './mxv-pthreads -m 8000 -n 4000 -t 1'
Process pid 2750071, ppid 2750069, pgrp 2749860, sid 2742080
Current working directory: <apath>
Collector version: `2.40.00'; experiment version 12.4 (64-bit)
Host `<the-host-name>', OS `Linux <version>', page size 4096,
                     architecture `x86_64'
  4 CPUs, clock speed 2294 MHz.
  Memory: 3506491 pages @  4096 = 13697 MB.
Data collection parameters:
  Clock-profiling, interval = 997 microsecs.
  Periodic sampling, 1 secs.
  Follow descendant processes from: fork|exec|combo

Experiment started <date and time>

Experiment Ended: 9.801216173
Data Collection Duration: 9.801216173
@end verbatim
@end smallexample

The output above may assist in troubleshooting, or to verify some of the
operational conditions and we recommend to include this command when
generating a profile.

@IndexSubentry{Options, @code{-C}}
Related to this command there is a useful option to record comment(s) in
an experiment.
To this end, use the @samp{-C} option on the @CollectApp{} tool to
specify a comment string.  Up to ten comment lines can be included.
These comments are displayed with the @command{header} command on
the @DisplayText{} tool.

@IndexSubentry{Options,  @code{-overview}}
@IndexSubentry{Commands, @code{overview}}
The @command{overview} command displays information on the experiment(s) and
also shows a summary of the values for the metric(s) used.  This is an example
how to use it on the newly created experiment directory:

@cartouche
@smallexample
$ gprofng display text -overview mxv.1.thr.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Experiment(s):

Experiment      :mxv.1.thr.er
  Target        : './mxv-pthreads -m 8000 -n 4000 -t 1'
  Host          : <hostname> (<ISA>, Linux <version>)
  Start Time    : <date and time>
  Duration      : 9.801 Seconds

Metrics:

  Experiment Duration (Seconds): [9.801]
  Clock Profiling
    [X]Total CPU Time - totalcpu (Seconds): [*9.703]

Notes: '*' indicates hot metrics, '[X]' indicates currently enabled
       metrics.
       The metrics command can be used to change selections. The
       metric_list command lists all available metrics.
@end verbatim
@end smallexample

This command provides a dashboard overview that helps to easily identify
where the time is spent and in case hardware event counters are used, it
shows their total values.

@c -- A new node --------------------------------------------------------------
@node       Control the Sampling Frequency
@subsection Control the Sampling Frequency
@c ----------------------------------------------------------------------------

@cindex Sampling frequency
So far we did not go into details on the frequency of the sampling process,
but in some cases it is useful to change the default of 10 milliseconds.

The advantage of increasing the sampling frequency is that functions that
do not take much time per invocation are more accurately captured.  The
downside is that more data is gathered.  This has an impact on the overhead
of the collection process and more disk space is required.

In general this is not an immediate concern, but with heavily threaded
applications that run for an extended period of time, increasing the
frequency may have a more noticeable impact.

@IndexSubentry{Options, @code{-p}}
The @code{-p} option on the @CollectApp{} tool is used to enable or disable
clock based profiling, or to explicitly set the sampling rate.
@cindex Sampling interval
This option takes one of the following keywords:

@table @code

@item off
Disable clock based profiling.

@item on
Enable clock based profiling with a per thread sampling interval of 10 ms.
This is the default.

@item lo
Enable clock based profiling with a per thread sampling interval of 100 ms.

@item hi
Enable clock based profiling with a per thread sampling interval of 1 ms.

@item @var{value}
@cindex Sampling interval
Enable clock based profiling with a per thread sampling interval of
@var{value}.

@end table

It may seem unnecessary to have an option to disable clock based profiling,
but there is a good reason to support this.
By default, clock profiling  is enabled when conducting hardware event counter
experiments (@xref{Profile Hardware Event Counters}).
With the @code{-p off} option, this can be disabled.

If an explicit value is set for the sampling, the number can be an integer or
a floating-point number.
A suffix of @samp{u} for microseconds, or @samp{m} for milliseconds is
supported.  If no suffix is used, the value is assumed to be in milliseconds.
For example, the following command sets the sampling rate to
5123.4 microseconds:

@cartouche
@smallexample
$ gprofng collect app -p 5123.4u ./mxv-pthreads -m 8000 -n 4000 -t 1
@end smallexample
@end cartouche

If the value is smaller than the clock profiling minimum, a warning message
is issued and it is set to the minimum.
In case it is not a multiple of the clock profiling resolution, it is
silently rounded down to the nearest multiple of the clock resolution.
If the value exceeds the clock profiling maximum, is negative, or zero, an
error is reported.

@IndexSubentry{Options,  @code{-header}}
@IndexSubentry{Commands, @code{header}}
@noindent
Note that the @code{header} command echoes the sampling rate used.

@c -- A new node --------------------------------------------------------------
@node       Information on Load Objects
@subsection Information on Load Objects
@c ----------------------------------------------------------------------------

It may happen that the function view shows a function that is not known to
the user.  This can easily happen with library functions for example.
Luckily there are three commands that come in handy then.

@IndexSubentry{Options,  @code{-objects}}
@IndexSubentry{Commands, @code{objects}}
@IndexSubentry{Options,  @code{-fsingle}}
@IndexSubentry{Commands, @code{fsingle}}
@IndexSubentry{Options,  @code{-fsummary}}
@IndexSubentry{Commands, @code{fsummary}}
These commands are @command{objects}, @command{fsingle}, and
@command{fsummary}.  They provide details on
@cindex Load objects
load objects (@xref{Load Objects and Functions}).

The @command{objects} command lists all load objects that have been referenced
during the performance experiment.
Below we show the command and the result for our profile job.  Like before,
some path names in the output have been shortened and replaced by the
@IndexSubentry{Miscellaneous, @code{<apath>}}
@code{<apath>} symbol that represents an absolute directory path.

@cartouche
@smallexample
$ gprofng display text -objects mxv.1.thr.er
@end smallexample
@end cartouche

The output includes the name and path of the target executable:

@smallexample
@verbatim
<Unknown> (<Unknown>)
<mxv-pthreads> (<apath>/mxv-pthreads)
<libdl-2.28.so> (/usr/lib64/libdl-2.28.so)
<librt-2.28.so> (/usr/lib64/librt-2.28.so)
<libc-2.28.so> (/usr/lib64/libc-2.28.so)
<libpthread-2.28.so> (/usr/lib64/libpthread-2.28.so)
<libm-2.28.so> (/usr/lib64/libm-2.28.so)
<libgp-collector.so> (/usr/lib64/gprofng/libgp-collector.so)
<ld-2.28.so> (/usr/lib64/ld-2.28.so)
<DYNAMIC_FUNCTIONS> (DYNAMIC_FUNCTIONS)
@end verbatim
@end smallexample

@IndexSubentry{Options,  @code{-fsingle}}
@IndexSubentry{Commands, @code{fsingle}}
The @command{fsingle} command may be used to get more details on a specific
entry in the function view, say.  For example, the command below provides
additional information on the @code{pthread_create} function shown in the
function overview.

@cartouche
@smallexample
$ gprofng display text -fsingle pthread_create mxv.1.thr.er
@end smallexample
@end cartouche

Below the output from this command.  It has been somewhat modified to match
the display requirements.

@smallexample
@verbatim
+ gprofng display text -fsingle pthread_create mxv.1.thr.er
pthread_create
        Exclusive Total CPU Time: 0.    (  0. %)
        Inclusive Total CPU Time: 0.001 (  0.0%)
                            Size:   258
                      PC Address: 8:0x00049f60
                     Source File: (unknown)
                     Object File: (unknown)
                     Load Object: /usr/lib64/gprofng/libgp-collector.so
                    Mangled Name:
                         Aliases:
@end verbatim
@end smallexample

In this table we not only see how much time was spent in this function, we
also see where it originates from.  In addition to this, the size and start
address are given as well.  If the source code location is known it is also
shown here.

@IndexSubentry{Options,  @code{-fsummary}}
@IndexSubentry{Commands, @code{fsummary}}
The related @code{fsummary} command displays the same information as
@code{fsingle}, but for all functions in the function overview,
including @code{<Total>}:

@cartouche
@smallexample
$ gprofng display text -fsummary mxv.1.thr.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Functions sorted by metric: Exclusive Total CPU Time

<Total>
       Exclusive Total CPU Time: 9.703 (100.0%)
       Inclusive Total CPU Time: 9.703 (100.0%)
                           Size:     0
                     PC Address: 1:0x00000000
                    Source File: (unknown)
                    Object File: (unknown)
                    Load Object: <Total>
                   Mangled Name:
                        Aliases:

mxv_core
       Exclusive Total CPU Time: 9.226 ( 95.1%)
       Inclusive Total CPU Time: 9.226 ( 95.1%)
                           Size:    80
                     PC Address: 2:0x00001d56
                    Source File: <apath>/src/mxv.c
                    Object File: mxv.1.thr.er/archives/mxv-pthreads_ss_pf53V__5
                    Load Object: <apath>/mxv-pthreads
                   Mangled Name:
                        Aliases:

          ... etc ...
@end verbatim
@end smallexample

@c -- A new node --------------------------------------------------------------
@node    Support for Multithreading
@section Support for Multithreading
@c ----------------------------------------------------------------------------

In this chapter the support for multithreading is introduced and discussed.
As is shown below, nothing needs to be changed when collecting the performance
data.

The difference is that additional commands are available to get more
information on the multithreading details, plus that several filters allow
the user to zoom in on specific threads.

@c -- A new node --------------------------------------------------------------
@node       Creating a Multithreading Experiment
@subsection Creating a Multithreading Experiment
@c ----------------------------------------------------------------------------

We demonstrate the support for multithreading using the same code and settings
as before, but this time 2 threads are used:

@cartouche
@smallexample
$ exe=mxv-pthreads
$ m=8000
$ n=4000
$ gprofng collect app -O mxv.2.thr.er ./$exe -m $m -n $n -t 2
@end smallexample
@end cartouche

First of all, in as far as @ProductName{} is concerned, no changes are needed.
Nothing special is needed to profile a multithreaded job when using
@ToolName{}.

The same is true when displaying the performance results.  The same commands
that were used before work unmodified.  For example, this is all that is
needed to get a function overview:

@cartouche
@smallexample
$ gprofng display text -limit 5 -functions mxv.2.thr.er
@end smallexample
@end cartouche

@noindent
This produces the following familiar looking output:

@smallexample
@verbatim
Print limit set to 5
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total   Incl. Total    Name
CPU           CPU
 sec.      %   sec.      %
9.464 100.00  9.464 100.00   <Total>
8.961  94.69  8.961  94.69   mxv_core
0.224   2.37  0.469   4.95   init_data
0.105   1.11  0.177   1.88   erand48_r
0.073   0.77  0.073   0.77   __drand48_iterate
@end verbatim
@end smallexample

@c -- A new node --------------------------------------------------------------
@node       Commands Specific to Multithreading
@subsection Commands Specific to Multithreading
@c ----------------------------------------------------------------------------

The function overview shown above shows the results aggregated over all the
threads.  The interesting new element is that we can also look at the
performance data for the individual threads.

@IndexSubentry{Options,  @code{-thread_list}}
@IndexSubentry{Commands, @code{thread_list}}
The @command{thread_list} command displays how many threads have been used:

@cartouche
@smallexample
$ gprofng display text -thread_list mxv.2.thr.er
@end smallexample
@end cartouche

This produces the following output, showing that three threads have
been used:

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 all     3
@end verbatim
@end smallexample

The output confirms there is one experiment and that by default all
threads are selected.

It may seem surprising to see three threads here, since we used the
@code{-t 2} option, but it is common for a Pthreads program to use one
additional thread.
Typically, there is one main thread that runs from start to finish.
It handles the sequential portions of the code, as well as thread
management related tasks.
It is no different in the example code.  At some point, the main thread
creates and activates the two threads that perform the multiplication
of the matrix with the vector.  Upon completion of this computation,
the main thread continues.

@IndexSubentry{Options,  @code{-threads}}
@IndexSubentry{Commands, @code{threads}}
The @command{threads} command is simple, yet very powerful.  It shows the
total value of the metrics for each thread.

@cartouche
@smallexample
$ gprofng display text -threads mxv.2.thr.er
@end smallexample
@end cartouche

@noindent
The command above produces the following overview:

@smallexample
@verbatim
Objects sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
9.464 100.00   <Total>
4.547  48.05   Process 1, Thread 3
4.414  46.64   Process 1, Thread 2
0.502   5.31   Process 1, Thread 1
@end verbatim
@end smallexample

The first line gives the total CPU time accumulated over the threads
selected.  This is followed by the metric value(s) for each thread.

From this it is clear that the main thread is responsible for a
little over 5% of the total CPU time, while the other two threads
take 47-48% each.

This view is ideally suited to verify if there are any load balancing
issues and also to find the most time consuming thread(s).

@IndexSubentry{Filters, Thread selection}
While useful, often more information than this is needed.  This is
@IndexSubentry{Options,  @code{-thread_select}}
@IndexSubentry{Commands, @code{thread_select}}
where the thread selection filter comes in.  Through the
@command{thread_select}
command, one or more threads may be selected.
@xref{The Selection List} how to define the selection list.

Since it is most common to use this command in a script, we do so as
well here.  Below the script we are using:

@cartouche
@smallexample
# Define the metrics
metrics e.%totalcpu
# Limit the output to 5 lines
limit 5
# Get the function overview for thread 1
thread_select 1
functions
# Get the function overview for thread 2
thread_select 2
functions
# Get the function overview for thread 3
thread_select 3
functions
@end smallexample
@end cartouche

The definition of the metrics and the output limit have been shown and
explained earlier.  The new command to focus on is @command{thread_select}.

This command takes a list (@xref{The Selection List}) to select specific
threads.  In this case, the individual thread numbers that were
obtained earlier with the @command{thread_list} command are selected.

This restricts the output of the @command{functions} command to the thread
number(s) specified.  This means that the script above shows which
function(s) each thread executes and how much CPU time they consumed.
Both the exclusive timings and their percentages are given.

Note that technically this command is a filter and persistent.  The
selection remains active until changed through another thread selection
command, or when it is reset with the @samp{all} selection list.

@noindent
This is the relevant part of the output for the first thread:

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 1       3
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
0.502 100.00   <Total>
0.224  44.64   init_data
0.105  20.83   erand48_r
0.073  14.48   __drand48_iterate
0.067  13.29   drand48
@end verbatim
@end smallexample

As usual, the comment lines are echoed.  This is followed by a confirmation
of the selection.  The first table shows that one experiment is loaded and
that thread 1 out of the three threads has been selected.  What is
displayed next is the function overview for this particular thread.  Due to
the @code{limit 5} command, there are only five functions in this list.

Clearly, this thread handles the data initialization part and as we know
from the call tree output, function @code{init_data} executes the 3 other
functions shown in this profile.

Below are the overviews for threads 2 and 3 respectively.  It is seen that all
of the CPU time is spent in function @code{mxv_core} and that this time
is approximately the same for both threads.

@smallexample
@verbatim
# Get the function overview for thread 2
Exp Sel Total
=== === =====
  1 2       3
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
4.414 100.00   <Total>
4.414 100.00   mxv_core
0.      0.     <static>@0x48630 (<libgp-collector.so>)
0.      0.     driver_mxv
0.      0.     start_thread

# Get the function overview for thread 3
Exp Sel Total
=== === =====
  1 3       3
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
4.547 100.00   <Total>
4.547 100.00   mxv_core
0.      0.     <static>@0x48630 (<libgp-collector.so>)
0.      0.     driver_mxv
0.      0.     start_thread
@end verbatim
@end smallexample

When analyzing the performance of a multithreaded application, it is sometimes
useful to know whether threads have mostly executed on the same core, say, or
if they have wandered across multiple cores.  This sort of stickiness is
usually referred to as
@cindex Thread affinity
@emph{thread affinity}.

Similar to the commands for the threads, there are several commands related
to the usage of the cores, or @emph{CPUs} as they are called in @ToolName{}
(@xref{The Concept of a CPU in gprofng}).

@IndexSubentry{Options,  @code{-cpu_list}}
@IndexSubentry{Commands, @code{cpu_list}}
Similar to the @command{thread_list} command, the @command{cpu_list} command
displays how many CPUs have been used.
@IndexSubentry{Options,  @code{-cpus}}
@IndexSubentry{Commands, @code{cpus}}
The equivalent of the @command{threads} threads command, is the @command{cpus}
command, which shows the numbers of the CPUs that were used and the metric
values for each one of them.  Both commands are demonstrated below.

@cartouche
@smallexample
$ gprofng display text -cpu_list -cpus mxv.2.thr.er
@end smallexample
@end cartouche

@noindent
This command produces the following output:

@smallexample
@verbatim
+ gprofng display text -cpu_list -cpus mxv.2.thr.er
Exp Sel Total
=== === =====
  1 all     4
Objects sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
9.464 100.00   <Total>
4.414  46.64   CPU 2
2.696  28.49   CPU 0
1.851  19.56   CPU 1
0.502   5.31   CPU 3
@end verbatim
@end smallexample

The first table shows that there is only one experiment and that all of the
four CPUs have been selected.  The second table shows the exclusive metrics
for each of the CPUs that have been used.

As also echoed in the output, the data is sorted with respect to the
exclusive CPU time, but it is very easy to sort the data by the CPU id
@IndexSubentry{Options, -sort}
@IndexSubentry{Commands, sort}
by using the @command{sort} command:

@cartouche
@smallexample
$ gprofng display text -cpu_list -sort name -cpus mxv.2.thr.er
@end smallexample
@end cartouche

@noindent
With the @command{sort} added, the output is as follows:

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 all     4
Current Sort Metric: Name ( name )
Objects sorted by metric: Name

Excl. Total    Name
CPU
 sec.      %
9.464 100.00   <Total>
2.696  28.49   CPU 0
1.851  19.56   CPU 1
4.414  46.64   CPU 2
0.502   5.31   CPU 3
@end verbatim
@end smallexample

While the table with thread times shown earlier may point at a load imbalance
in the application, this overview has a different purpose.

For example, we see that 4 CPUs have been used, but we know that the
application uses 3 threads only.
We will now demonstrate how filters can be used to help answer the
question why 4 CPUs are used, while the application has 3 threads only.
This means that at least one thread has executed on more than one CPU.

Recall the thread level timings:

@smallexample
@verbatim
Excl. Total    Name
CPU
 sec.      %
9.464 100.00   <Total>
4.547  48.05   Process 1, Thread 3
4.414  46.64   Process 1, Thread 2
0.502   5.31   Process 1, Thread 1
@end verbatim
@end smallexample

Compared to the CPU timings above, it seems very likely that thread 3 has
used more than one CPU, because the thread and CPU timings are the same
for both other threads.

The command below selects thread number 3 and then requests the CPU
utilization for this thread:

@cartouche
@smallexample
$ gprofng display text -thread_select 3 -sort name -cpus mxv.2.thr.er
@end smallexample
@end cartouche

The output shown below confirms that thread 3 is selected and then displays
the CPU(s) that have been used by this thread:

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 3       3

Objects sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
4.547 100.00   <Total>
2.696  59.29   CPU 0
1.851  40.71   CPU 1
@end verbatim
@end smallexample

The results show that this thread has used CPU 0 nearly 60% of the time
and CPU 1 for the remaining 40%.

To confirm that this is the only thread that has used more than one CPU, the
same approach can be used for threads 1 and 2:

@smallexample
@verbatim
$ gprofng display text -thread_select 1 -cpus mxv.2.thr.er
Exp Sel Total
=== === =====
  1 1       3
Objects sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
0.502 100.00   <Total>
0.502 100.00   CPU 3
@end verbatim
@end smallexample

@smallexample
@verbatim
$ gprofng display text -thread_select 2 -cpus mxv.2.thr.er
Exp Sel Total
=== === =====
  1 2       3
Objects sorted by metric: Exclusive Total CPU Time

Excl. Total    Name
CPU
 sec.      %
4.414 100.00   <Total>
4.414 100.00   CPU 2
@end verbatim
@end smallexample

@noindent
The output above shows that indeed threads 1 and 2 each have used a single
CPU only.

@c -- A new node --------------------------------------------------------------
@node    View Multiple Experiments
@section View Multiple Experiments
@c ----------------------------------------------------------------------------

One thing we did not cover sofar is that @ToolName{} fully supports the
analysis of multiple experiments.  The @DisplayText{} tool accepts a list of
experiments.  The data can either be aggregated across the experiments, or
used in a comparison.

The default is to aggregate the metric values across the experiments that have
been loaded.  The @command{compare} command can be used to enable the
@IndexSubentry{Options, @code{-compare}}
@IndexSubentry{Commands, @code{compare}}
comparison of results.

In this section both modes are illustrated with an example.

@c -- A new node --------------------------------------------------------------
@node       Aggregation of Experiments
@subsection Aggregation of Experiments
@c ----------------------------------------------------------------------------

If the data for multiple experiments is aggregrated, the @DisplayText{} tool
shows the combined results.
For example, below is the script to show the function view for the data
aggregated over two experiments, drop the first experiment and then show
the function view for the second experiment only.
We will call it @file{my-script-agg}.

@cartouche
@smallexample
# Define the metrics
metrics e.%totalcpu
# Limit the output to 5 lines
limit 5
# Get the list with experiments
experiment_list
# Get the function overview for all
functions
# Drop the first experiment
drop_exp mxv.2.thr.er
# Get the function overview for exp #2
functions
@end smallexample
@end cartouche

@IndexSubentry{Options,  @code{-experiment_list}}
@IndexSubentry{Commands, @code{experiment_list}}
With the exception of the @command{experiment_list} command, all commands
used have been discussed earlier.

The @command{experiment_list} command provides a list of the experiments
that have been loaded.  This may be used to get the experiment IDs and
to verify the correct experiments are loaded for the aggregation.

@noindent
Below is an example that loads two experiments and uses the above
script to display different function views.

@cartouche
@smallexample
$ gprofng display text -script my-script-agg mxv.2.thr.er mxv.4.thr.er
@end smallexample
@end cartouche

@noindent
This produces the following output:

@smallexample
@verbatim
# Define the metrics
Current metrics: e.%totalcpu:name
Current Sort Metric: Exclusive Total CPU Time ( e.%totalcpu )
# Limit the output to 5 lines
Print limit set to 5
# Get the list with experiments
ID Sel     PID Experiment
== === ======= ============
 1 yes 1339450 mxv.2.thr.er
 2 yes 3579561 mxv.4.thr.er
# Get the function overview for all
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total     Name
CPU
  sec.      %
20.567 100.00   <Total>
19.553  95.07   mxv_core
 0.474   2.30   init_data
 0.198   0.96   erand48_r
 0.149   0.72   drand48

# Drop the first experiment
Experiment mxv.2.thr.er has been dropped
# Get the function overview for exp #2
Functions sorted by metric: Exclusive Total CPU Time

Excl. Total     Name
CPU
  sec.      %
11.104 100.00   <Total>
10.592  95.39   mxv_core
 0.249   2.24   init_data
 0.094   0.84   erand48_r
 0.082   0.74   drand48
@end verbatim
@end smallexample

The first five lines should look familiar.  The five lines following echo
the comment line in the script and show the overview of the experiments.
This confirms two experiments have been loaded and that both are active.
This is followed by the function overview.  The timings have been summed
up and the percentages are adjusted accordingly.

@c -- A new node --------------------------------------------------------------
@node       Comparison of Experiments
@subsection Comparison of Experiments
@c ----------------------------------------------------------------------------

The support for multiple experiments really shines in comparison mode.
@cindex Compare experiments
In comparison mode, the data for the various experiments is shown side by
side, as illustrated below where we compare the results for the multithreaded
experiments using two and four threads respectively.

This
feature is controlled through the
@IndexSubentry{Options,  @code{-compare}}
@IndexSubentry{Commands, @code{compare}}
@code{compare} command.

The comparison mode is enabled through @command{compare on} and with
@command{compare off} it is disabled again.
In addition to @samp{on}, or @samp{off}, this command also supports
the @samp{delta} and @samp{ratio} keywords.

This is the script that will be used in our example.  It sets the comparison
mode to @samp{on}:

@smallexample
@verbatim
# Define the metrics
metrics e.%totalcpu
# Limit the output to 5 lines
limit 5
# Set the comparison mode to differences
compare on
# Get the function overview
functions
@end verbatim
@end smallexample

Assuming this script file is called @file{my-script-comp}, this is how
it is used to display the differences:

@cartouche
@smallexample
$ gprofng display text -script my-script-comp mxv.2.thr.er mxv.4.thr.er
@end smallexample
@end cartouche

@noindent
This produces the output shown below.  The data for the first experiment
is shown as absolute numbers.  The timings for the other experiment are
shown as a delta relative to these reference numbers:

@smallexample
@verbatim

mxv.2.thr.er  mxv.4.thr.er
Excl. Total   Excl. Total     Name
CPU           CPU
 sec.      %    sec.      %
9.464 100.00  11.104 100.00   <Total>
8.961  94.69  10.592  95.39   mxv_core
0.224   2.37   0.249   2.24   init_data
0.105   1.11   0.094   0.84   erand48_r
0.073   0.77   0.060   0.54   __drand48_iterate
@end verbatim
@end smallexample

This table is already helpful to more easily compare (two) profiles, but
there is more that we can do here.

By default, in comparison mode, all measured values are shown.  Often
profiling is about comparing performance data.  It is therefore
sometimes more useful to look at differences or ratios, using one
experiment as a reference.

The values shown are relative to this difference.  For example if a ratio
is below one, it means the reference value was higher.

In the example below, we use the same two experiments used in the comparison
above.  The script is also nearly identical.  The only change is that we now
use the @samp{delta} keyword.

As before, the number of lines is restricted to 5 and we focus on
the exclusive timings plus percentages.  For the comparison part we are
interested in the differences.

This is the script that produces such an overview:

@smallexample
@verbatim
# Define the metrics
metrics e.%totalcpu
# Limit the output to 5 lines
limit 5
# Set the comparison mode to differences
compare delta
# Get the function overview
functions
@end verbatim
@end smallexample

Assuming this script file is called @file{my-script-comp2}, this is how we
get the table displayed on our screen:

@cartouche
@smallexample
$ gprofng display text -script my-script-comp2 mxv.2.thr.er mxv.4.thr.er
@end smallexample
@end cartouche

Leaving out some of the lines printed, but we have seen before, we get
the following table:

@smallexample
@verbatim
mxv.2.thr.er  mxv.4.thr.er
Excl. Total   Excl. Total     Name
CPU           CPU
 sec.      %   delta      %
9.464 100.00  +1.640 100.00   <Total>
8.961  94.69  +1.631  95.39   mxv_core
0.224   2.37  +0.025   2.24   init_data
0.105   1.11  -0.011   0.84   erand48_r
0.073   0.77  -0.013   0.54   __drand48_iterate
@end verbatim
@end smallexample

It is now easier to see that the CPU times for the most time consuming
functions in this code are practically the same.

It is also possible to show ratio's through the @command{compare ratio}
@IndexSubentry{Options, @code{-compare}}
@IndexSubentry{Commands, @code{compare}}
command.  The first colum is used as a reference and the values for
the other columns with metrics are derived by dividing the value by
the reference.  The result for such a comparison is shown below:

@smallexample
@verbatim
mxv.2.thr.er  mxv.4.thr.er
Excl. Total   Excl. Total CPU    Name
CPU
 sec.      %      ratio      %
9.464 100.00  x   1.173 100.00   <Total>
8.961  94.69  x   1.182  95.39   mxv_core
0.224   2.37  x   1.111   2.24   init_data
0.105   1.11  x   0.895   0.84   erand48_r
0.073   0.77  x   0.822   0.54   __drand48_iterate
@end verbatim
@end smallexample

Note that the comparison feature is supported at the function, source, and
disassembly level.  There is no practical limit on the number of experiments
that can be used in a comparison.

@c -- A new node --------------------------------------------------------------
@node    Profile Hardware Event Counters
@section Profile Hardware Event Counters
@c ----------------------------------------------------------------------------

Many processors provide a set of hardware event counters and @ToolName{}
provides support for this feature.
@xref{Hardware Event Counters Explained} for those readers that are not
familiar with such counters and like to learn more.

In this section we explain how to get the details on the event counter
support for the processor used in the experiment(s), and show several
examples.

@c -- A new node --------------------------------------------------------------
@node       Getting Information on the Counters Supported
@subsection Getting Information on the Counters Supported
@c ----------------------------------------------------------------------------

The first step is to check if the processor used for the experiments is
supported by @ToolName{}.
@IndexSubentry{Options, @code{-h}}
The @code{-h} option on @CollectApp{} will show the event counter
information:

@cartouche
@smallexample
$ gprofng collect app -h
@end smallexample
@end cartouche

In case the counters are supported, a list with the events is printed.
Otherwise, a warning message will be issued.

For example, below we show this command and the output on an Intel Xeon
Platinum 8167M (aka ``Skylake'') processor.  The output has been split
into several sections and each section is commented upon separately.

@smallexample
@verbatim
Run "gprofng collect app --help" for a usage message.

Specifying HW counters on `Intel Arch PerfMon v2 on Family 6 Model 85'
(cpuver=2499):

  -h {auto|lo|on|hi}
	turn on default set of HW counters at the specified rate
  -h <ctr_def> [-h <ctr_def>]...
  -h <ctr_def>[,<ctr_def>]...
	specify HW counter profiling for up to 4 HW counters
@end verbatim
@end smallexample

The first line shows how to get a usage overview.  This is followed by
some information on the target processor.
The next five lines explain in what ways the @code{-h} option can be
used to define the events to be monitored.

The first version shown above enables a default set of counters.  This
default depends on the processor this command is executed on.  The
keyword following the @code{-h} option defines the sampling rate:

@table @code

@item auto
Match the sample rate of used by clock profiling.  If the latter is disabled,
Use a per thread sampling rate of approximately 100 samples per second.
This setting is the default and preferred.

@item on
Use a per thread sampling rate of approximately 100 samples per second.

@item lo
Use a per thread sampling rate of approximately 10 samples per second.

@item hi
Use a per thread sampling rate of approximately 1000 samples per second.

@end table

The second and third variant define the events to be monitored.  Note
that the number of simultaneous events supported is printed.  In this
case we can monitor four events in a single profiling job.

It is a matter of preference whether you like to use the @code{-h}
option for each event, or use it once, followed by a comma separated
list.

There is one slight catch though.  The counter definition below has
mandatory comma (@code{,}) between the event and the rate.  While a
default can be used for the rate, the comma cannot be omitted.
This may result in a somewhat awkward counter definition in case
the default sampling rate is used.

For example, the following two commands are equivalent.  Note
the double comma in the second command.  This is not a typo.

@cartouche
@smallexample
$ gprofng collect app -h cycles -h insts ...
$ gprofng collect app -h cycles,,insts ...
@end smallexample
@end cartouche

In the first command this comma is not needed, because a
comma (``@code{,}'') immediately followed by white space may
be omitted.

This is why we prefer the this syntax and in the remainder will
use the first version of this command.

@IndexSubentry{Hardware event counters, counter definition}
The counter definition takes an event name, plus optionally one or
more attributes, followed by a comma, and optionally the sampling rate.
The output section below shows the formal definition.

@cartouche
@smallexample
  <ctr_def> == <ctr>[[~<attr>=<val>]...],[<rate>]
@end smallexample
@end cartouche

The printed help then explains this syntax.  Below we have summarized
and expanded this output:

@table @code

@item @var{<ctr>}
The counter name must be selected from the available counters listed
as part of the output printed with the @code{-h} option.
On most systems, if a counter is not listed, it may still be specified
by its numeric value.

@item @var{~<attr>=<val>}
This is an optional attribute that depends on the processor.  The list
of supported attributes is printed in the output.  Examples of
attributes are ``user'', or ``system''.  The value can given in decimal
or hexadecimal format.
Multiple attributes may be specified, and each must be preceded
by a ~.

@item @var{<rate>}

The sampling rate is one of the following:

@table @code

@item auto
This is the default and matches the rate used by clock profiling.
If clock profiling is disabled, use @samp{on}.

@item on
Set the per thread maximum sampling rate to ~100 samples/second

@item lo
Set the per thread maximum sampling rate to ~10 samples/second

@item hi
Set the per thread maximum sampling rate to ~1000 samples/second

@item @var{<interval>}
Define the sampling interval.
@xref{Control the Sampling Frequency} how to define this.

@end table

@end table

After the section with the formal definition of events and counters, a
processor specific list is displayed.  This part starts with an overview
of the default set of counters and the aliased names supported
@emph{on this specific processor}.

@smallexample
@verbatim
Default set of HW counters:

    -h cycles,,insts,,llm

Aliases for most useful HW counters:

 alias    raw name                   type units regs description

 cycles   unhalted-core-cycles   CPU-cycles 0123 CPU Cycles
 insts    instruction-retired        events 0123 Instructions Executed
 llm      llc-misses                 events 0123 Last-Level Cache Misses
 br_msp   branch-misses-retired      events 0123 Branch Mispredict
 br_ins   branch-instruction-retired events 0123 Branch Instructions
@end verbatim
@end smallexample

@noindent
The definitions given above may or may not be available on other processors.

The table above shows the default set of counters defined for this processor,
and the aliases.  For each alias the full ``raw'' name is given, plus the
unit of the number returned by the counter (CPU cycles, or a raw count),
the hardware counter the event is allowed to be mapped onto, and a short
description.

The last part of the output contains all the events that can be monitored:

@smallexample
@verbatim
Raw HW counters:

    name                                type      units regs description

    unhalted-core-cycles                     CPU-cycles 0123
    unhalted-reference-cycles                    events 0123
    instruction-retired                          events 0123
    llc-reference                                events 0123
    llc-misses                                   events 0123
    branch-instruction-retired                   events 0123
    branch-misses-retired                        events 0123
    ld_blocks.store_forward                      events 0123
    ld_blocks.no_sr                              events 0123
    ld_blocks_partial.address_alias              events 0123
    dtlb_load_misses.miss_causes_a_walk          events 0123
    dtlb_load_misses.walk_completed_4k           events 0123

    <many lines deleted>

    l2_lines_out.silent                          events 0123
    l2_lines_out.non_silent                      events 0123
    l2_lines_out.useless_hwpf                    events 0123
    sq_misc.split_lock                           events 0123
@end verbatim
@end smallexample

As can be seen, these names are not always easy to correlate to a specific
event of interest.  The processor manual should provide more clarity on this.

@c -- A new node --------------------------------------------------------------
@node       Examples Using Hardware Event Counters
@subsection Examples Using Hardware Event Counters
@c ----------------------------------------------------------------------------

The previous section may give the impression that these counters are hard to
use, but as we will show now, in practice it is quite simple.

With the information from the @code{-h} option, we can easily set up our first
event counter experiment.

We start by using the default set of counters defined for our processor and we
use 2 threads:

@cartouche
@smallexample
$ exe=mxv-pthreads
$ m=8000
$ n=4000
$ exp=mxv.hwc.def.2.thr.er
$ gprofng collect app -O $exp -h auto ./$exe -m $m -n $n -t 2
@end smallexample
@end cartouche

@IndexSubentry{Options, @code{-h}}
@IndexSubentry{Hardware event counters, @code{auto} option}
The new option here is @code{-h auto}.  The @code{auto} keyword enables
hardware event counter profiling and selects the default set of counters
defined for this processor.

As before, we can display the information, but there is one practical hurdle
to take.  Unless we like to view all metrics recorded, we would need to know
the names of the events that have been enabled.  This is tedious and also not
portable in case we would like to repeat this experiment on another processor.

@IndexSubentry{Hardware event counters, @code{hwc} metric}
This is where the special @code{hwc} metric comes very handy.  It
automatically expands to the active set of hardware event counters used
in the experiment(s).

With this, it is very easy to display the event counter values.  Note that
although the regular clock based profiling was enabled, we only want to see
the counter values.  We also request to see the percentages and limit the
output to the first 5 lines:

@cartouche
@smallexample
$ exp=mxv.hwc.def.2.thr.er
$ gprofng display text -metrics e.%hwc -limit 5 -functions $exp
@end smallexample
@end cartouche

@smallexample
@verbatim
Current metrics: e.%cycles:e+%insts:e+%llm:name
Current Sort Metric: Exclusive CPU Cycles ( e.%cycles )
Print limit set to 5
Functions sorted by metric: Exclusive CPU Cycles

Excl. CPU     Excl. Instructions  Excl. Last-Level   Name
Cycles        Executed            Cache Misses
 sec.      %                  %                 %
2.691 100.00  7906475309 100.00   122658983 100.00   <Total>
2.598  96.54  7432724378  94.01   121745696  99.26   mxv_core
0.035   1.31   188860269   2.39       70084   0.06   erand48_r
0.026   0.95    73623396   0.93      763116   0.62   init_data
0.018   0.66    76824434   0.97       40040   0.03   drand48
@end verbatim
@end smallexample

As we have seen before, the first few lines echo the settings.
This includes a list with the hardware event counters used by
default.

The table that follows makes it very easy to get an overview where the
time is spent and how many of the target events have occurred.

As before, we can drill down deeper and see the same metrics at the source
line and instruction level.  Other than using @code{hwc} in the metrics
definitions, nothing has changed compared to the previous examples:

@cartouche
@smallexample
$ exp=mxv.hwc.def.2.thr.er
$ gprofng display text -metrics e.hwc -source mxv_core $exp
@end smallexample
@end cartouche

This is the relevant part of the output.  Since the lines get very long,
we have somewhat modified the lay-out:

@smallexample
@verbatim
   Excl. CPU Excl.        Excl.
   Cycles    Instructions Last-Level
    sec.     Executed     Cache Misses
                                         <Function: mxv_core>
   0.                 0          0   32. void __attribute__ ((noinline))
                                         mxv_core(...)
   0.                 0          0   33. {
   0.                 0          0   34.   for (uint64_t i=...) {
   0.                 0          0   35.     double row_sum = 0.0;
## 1.872     7291879319   88150571   36.     for (int64_t j=0; j<n; j++)
   0.725      140845059   33595125   37.        row_sum += A[i][j]*b[j];
   0.                 0          0   38.     c[i] = row_sum;
                                     39.    }
   0.                 0          0   40. }
@end verbatim
@end smallexample

In a smiliar way we can display the event counter values at the instruction
level.  Again we have modified the lay-out due to page width limitations:

@cartouche
@smallexample
$ exp=mxv.hwc.def.2.thr.er
$ gprofng display text -metrics e.hwc -disasm mxv_core $exp
@end smallexample
@end cartouche

@smallexample
@verbatim
   Excl. CPU Excl.        Excl.
   Cycles    Instructions Last-Level
    sec.     Executed     Cache Misses
                                                <Function: mxv_core>
   0.                 0          0  [33] 4021ba: mov   0x8(%rsp),%r10
                                    34.   for (uint64_t i=...) {
   0.                 0          0  [34] 4021bf: cmp   %rsi,%rdi
   0.                 0          0  [34] 4021c2: jbe   0x37
   0.                 0          0  [34] 4021c4: ret
                                    35.       double row_sum = 0.0;
                                    36.       for (int64_t j=0; j<n; j++)
                                    37.         row_sum += A[i][j]*b[j];
   0.                 0          0  [37] 4021c5: mov   (%r8,%rdi,8),%rdx
   0.                 0          0  [36] 4021c9: mov   $0x0,%eax
   0.                 0          0  [35] 4021ce: pxor  %xmm1,%xmm1
   0.002       12804230     321394  [37] 4021d2: movsd (%rdx,%rax,8),%xmm0
   0.141       60819025    3866677  [37] 4021d7: mulsd (%r9,%rax,8),%xmm0
   0.582       67221804   29407054  [37] 4021dd: addsd %xmm0,%xmm1
## 1.871     7279075109   87989870  [36] 4021e1: add   $0x1,%rax
   0.002       12804210      80351  [36] 4021e5: cmp   %rax,%rcx
   0.                 0          0  [36] 4021e8: jne   0xffffffffffffffea
                                    38.       c[i] = row_sum;
   0.                 0          0  [38] 4021ea: movsd %xmm1,(%r10,%rdi,8)
   0.                 0          0  [34] 4021f0: add   $0x1,%rdi
   0.                 0          0  [34] 4021f4: cmp   %rdi,%rsi
   0.                 0          0  [34] 4021f7: jb    0xd
   0.                 0          0  [35] 4021f9: pxor  %xmm1,%xmm1
   0.                 0          0  [36] 4021fd: test  %rcx,%rcx
   0.                 0      80350  [36] 402200: jne   0xffffffffffffffc5
   0.                 0          0  [36] 402202: jmp   0xffffffffffffffe8
                                    39.   }
                                    40. }
   0.                 0          0  [40]  402204:  ret
@end verbatim
@end smallexample

So far we have used the default settings for the event counters.  It is
quite straightforward to select specific counters.  For sake of the
example, let's assume we would like to count how many branch instructions
and retired memory load instructions that missed in the L1 cache have been
executed.  We also want to count these events with a high resolution.

This is the command to do so:

@cartouche
@smallexample
$ exe=mxv-pthreads
$ m=8000
$ n=4000
$ exp=mxv.hwc.sel.2.thr.er
$ hwc1=br_ins,hi
$ hwc2=mem_load_retired.l1_miss,hi
$ gprofng collect app -O $exp -h $hwc1 -h $hwc2 $exe -m $m -n $n -t 2
@end smallexample
@end cartouche

As before, we get a table with the event counts.  Due to the very
long name for the second counter, we have somewhat modified the
output.

@cartouche
@smallexample
$ gprofng display text -limit 10 -functions mxv.hwc.sel.2.thr.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Functions sorted by metric: Exclusive Total CPU Time
Excl.     Incl.     Excl. Branch  Excl.                 Name
Total     Total     Instructions  mem_load_retired.l1_miss
CPU sec.  CPU sec.                Events
2.597     2.597     1305305319    4021340               <Total>
2.481     2.481     1233233242    3982327               mxv_core
0.040     0.107       19019012       9003               init_data
0.028     0.052       23023048      15006               erand48_r
0.024     0.024       19019008       9004               __drand48_iterate
0.015     0.067       11011009       2998               drand48
0.008     0.010              0       3002               _int_malloc
0.001     0.001              0          0               brk
0.001     0.002              0          0               sysmalloc
0.        0.001              0          0               __default_morecore
@end verbatim
@end smallexample

@IndexSubentry{Options,  @code{-compare}}
@IndexSubentry{Commands, @code{compare}}
When using event counters, the values could be very large and it is not easy
to compare the numbers.  As we will show next, the @code{ratio} feature is
very useful when comparing such profiles.

To demonstrate this, we have set up another event counter experiment where
we would like to compare the number of last level cache miss and the number
of branch instructions executed when using a single thread, or two threads.

These are the commands used to generate the experiment directories:

@cartouche
@smallexample
$ exe=./mxv-pthreads
$ m=8000
$ n=4000
$ exp1=mxv.hwc.comp.1.thr.er
$ exp2=mxv.hwc.comp.2.thr.er
$ gprofng collect app -O $exp1 -h llm -h br_ins $exe -m $m -n $n -t 1
$ gprofng collect app -O $exp2 -h llm -h br_ins $exe -m $m -n $n -t 2
@end smallexample
@end cartouche

The following script has been used to get the tables.  Due to lay-out
restrictions, we have to create two tables, one for each counter.

@cartouche
@smallexample
# Limit the output to 5 lines
limit 5
# Define the metrics
metrics name:e.llm
# Set the comparison to ratio
compare ratio
functions
# Define the metrics
metrics name:e.br_ins
# Set the comparison to ratio
compare ratio
functions
@end smallexample
@end cartouche

Note that we print the name of the function first, followed by the counter
data.
The new element is that we set the comparison mode to @code{ratio}.  This
divides the data in a column by its counterpart in the reference experiment.

This is the command using this script and the two experiment directories as
input:

@cartouche
@smallexample
$ gprofng display text -script my-script-comp-counters \
  mxv.hwc.comp.1.thr.er \
  mxv.hwc.comp.2.thr.er
@end smallexample
@end cartouche

By design, we get two tables, one for each counter:

@smallexample
@verbatim
Functions sorted by metric: Exclusive Last-Level Cache Misses

                              mxv.hwc.comp.1.thr.er  mxv.hwc.comp.2.thr.er
Name                          Excl. Last-Level       Excl. Last-Level
                              Cache Misses           Cache Misses
                                                         ratio
 <Total>                      122709276              x   0.788
 mxv_core                     121796001              x   0.787
 init_data                       723064              x   1.055
 erand48_r                       100111              x   0.500
 drand48                          60065              x   1.167

Functions sorted by metric: Exclusive Branch Instructions

                              mxv.hwc.comp.1.thr.er  mxv.hwc.comp.2.thr.er
Name                          Excl. Branch           Excl. Branch
                              Instructions           Instructions
                                                       ratio
 <Total>                      1307307316             x 0.997
 mxv_core                     1235235239             x 0.997
 erand48_r                      23023033             x 0.957
 drand48                        20020009             x 0.600
 __drand48_iterate              17017028             x 0.882
@end verbatim
@end smallexample

A ratio less than one in the second column, means that this counter
value was smaller than the value from the reference experiment shown
in the first column.

This kind of presentation of the results makes it much easier to
quickly interpret the data.

We conclude this section with thread-level event counter overviews,
but before we go into this, there is an important metric we need to
mention.

@c -- TBD Explain <Total> for IPC

@IndexSubentry{Hardware event counters, IPC}
In case it is known how many instructions and CPU cycles have been executed,
the value for the IPC (``Instructions Per Clockycle'') can be computed.
@xref{Hardware Event Counters Explained}.
This is a derived metric that gives an indication how well the processor
is utilized.  The inverse of the IPC is called CPI.
@IndexSubentry{Hardware event counters, CPI}

The @DisplayText{} command automatically computes the IPC and CPI values
if an experiment contains the event counter values for the instructions
and CPU cycles executed.  These are part of the metric list and can be
displayed, just like any other metric.

@IndexSubentry{Options,  @code{-metric_list}}
@IndexSubentry{Commands, @code{metric_list}}
This can be verified through the @command{metric_list} command.  If we go
back to our earlier experiment with the default event counters, we get
the following result.

@cartouche
@smallexample
$ gprofng display text -metric_list mxv.hwc.def.2.thr.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Current metrics: e.totalcpu:i.totalcpu:e.cycles:e+insts:e+llm:name
Current Sort Metric: Exclusive Total CPU Time ( e.totalcpu )
Available metrics:
         Exclusive Total CPU Time: e.%totalcpu
         Inclusive Total CPU Time: i.%totalcpu
             Exclusive CPU Cycles: e.+%cycles
             Inclusive CPU Cycles: i.+%cycles
  Exclusive Instructions Executed: e+%insts
  Inclusive Instructions Executed: i+%insts
Exclusive Last-Level Cache Misses: e+%llm
Inclusive Last-Level Cache Misses: i+%llm
 Exclusive Instructions Per Cycle: e+IPC
 Inclusive Instructions Per Cycle: i+IPC
 Exclusive Cycles Per Instruction: e+CPI
 Inclusive Cycles Per Instruction: i+CPI
                             Size: size
                       PC Address: address
                             Name: name
@end verbatim
@end smallexample

Among the other metrics, we see the new metrics for the IPC and CPI
listed.

In the script below, we use this information and add the IPC and CPI
to the metrics to be displayed.  We also use a the thread filter to
display these values for the individual threads.

This is the complete script we have used.  Other than a different selection
of the metrics, there are no new features.

@cartouche
@smallexample
# Define the metrics
metrics e.insts:e.%cycles:e.IPC:e.CPI
# Sort with respect to cycles
sort e.cycles
# Limit the output to 5 lines
limit 5
# Get the function overview for all threads
functions
# Get the function overview for thread 1
thread_select 1
functions
# Get the function overview for thread 2
thread_select 2
functions
# Get the function overview for thread 3
thread_select 3
functions
@end smallexample
@end cartouche

In the metrics definition on the second line, we explicitly request the
counter values for the instructions (@code{e.insts}) and CPU cycles
(@code{e.cycles}) executed.  These names can be found in output from the
@IndexSubentry{Options, @code{-metric_list}}
@IndexSubentry{Commands, @code{metric_list}}
@command{metric_list} command above.
In addition to these metrics, we also request the IPC and CPI to be shown.

@IndexSubentry{Options, @code{-limit}}
@IndexSubentry{Commands, @code{limit}}
As before, we used the @command{limit} command to control the number of
functions displayed.  We then request an overview for all the threads,
followed by three sets of two commands to select a thread and display the
function overview.

The script above is used as follows:

@cartouche
@smallexample
$ gprofng display text -script my-script-ipc mxv.hwc.def.2.thr.er
@end smallexample
@end cartouche

@noindent
This script produces four tables.  We list them separately below,
and have left out the additional output.

@noindent
The first table shows the accumulated values across the three
threads that have been active.

@smallexample
@verbatim
Functions sorted by metric: Exclusive CPU Cycles

Excl.         Excl. CPU     Excl.  Excl.   Name
Instructions  Cycles        IPC    CPI
Executed       sec.      %
7906475309    2.691 100.00  1.473  0.679   <Total>
7432724378    2.598  96.54  1.434  0.697   mxv_core
 188860269    0.035   1.31  2.682  0.373   erand48_r
  73623396    0.026   0.95  1.438  0.696   init_data
  76824434    0.018   0.66  2.182  0.458   drand48
@end verbatim
@end smallexample

@noindent
This shows that IPC of this program is completely dominated
by function @code{mxv_core}.  It has a fairly low IPC value
of 1.43.

@noindent
The next table is for thread 1 and shows the values for the
main thread.

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 1       3
Functions sorted by metric: Exclusive CPU Cycles

Excl.         Excl. CPU     Excl.  Excl.   Name
Instructions  Cycles        IPC    CPI
Executed       sec.      %
473750931     0.093 100.00  2.552  0.392   <Total>
188860269     0.035  37.93  2.682  0.373   erand48_r
 73623396     0.026  27.59  1.438  0.696   init_data
 76824434     0.018  18.97  2.182  0.458   drand48
134442832     0.013  13.79  5.250  0.190   __drand48_iterate
@end verbatim
@end smallexample

@noindent
Although this thread hardly uses any CPU cycles, the overall IPC
of 2.55 is not all that bad.

@noindent
Last, we show the tables for threads 2 and 3:

@smallexample
@verbatim
Exp Sel Total
=== === =====
  1 2       3
Functions sorted by metric: Exclusive CPU Cycles

Excl.         Excl. CPU     Excl.  Excl.   Name
Instructions  Cycles        IPC    CPI
Executed       sec.      %
3716362189    1.298 100.00  1.435  0.697   <Total>
3716362189    1.298 100.00  1.435  0.697   mxv_core
         0    0.      0.    0.     0.      collector_root
         0    0.      0.    0.     0.      driver_mxv

Exp Sel Total
=== === =====
  1 3       3
Functions sorted by metric: Exclusive CPU Cycles

Excl.         Excl. CPU     Excl.  Excl.   Name
Instructions  Cycles        IPC    CPI
Executed       sec.      %
3716362189    1.300 100.00  1.433  0.698   <Total>
3716362189    1.300 100.00  1.433  0.698   mxv_core
         0    0.      0.    0.     0.      collector_root
         0    0.      0.    0.     0.      driver_mxv
@end verbatim
@end smallexample

It is seen that both execute the same number of instructions and
take about the same number of CPU cycles.  As a result, the IPC is
the same for both threads.

@c -- A new node --------------------------------------------------------------
@c TBD @node    Additional Features
@c TBD @section Additional Features
@c ----------------------------------------------------------------------------

@c -- A new node --------------------------------------------------------------
@c TBD @node    More Filtering Capabilities
@c TBD @subsection More Filtering Capabilities
@c ----------------------------------------------------------------------------

@c TBD Cover @code{samples} and @code{seconds}

@c -- A new node --------------------------------------------------------------
@node    Java Profiling
@section Java Profiling
@c ----------------------------------------------------------------------------

@IndexSubentry{Options, @code{-j}}
@IndexSubentry{Java profiling, @code{-j on/off}}
The @CollectApp{} command supports Java profiling.  The @code{-j on} option
can be used for this, but since this feature is enabled by default, there is
no need to set this explicitly.  Java profiling may be disabled through the
@code{-j off} option.

The program is compiled as usual and the experiment directory is created
similar to what we have seen before.  The only difference with a C/C++
application is that the program has to be explicitly executed by java.

For example, this is how to generate the experiment data for a Java
program that has the source code stored in file @code{Pi.java}:

@cartouche
@smallexample
$ javac Pi.java
$ gprofng collect app -j on -O pi.demo.er java Pi < pi.in
@end smallexample
@end cartouche

Regarding which java is selected to generate the data, @ToolName{}
first looks for the JDK in the path set in either the
@IndexSubentry{Java profiling, @code{JDK_HOME}}
@code{JDK_HOME} environment variable, or in the
@IndexSubentry{Java profiling, @code{JAVA_PATH}}
@code{JAVA_PATH} environment variable.  If neither of these variables is
set, it checks for a JDK in the search path (set in the PATH
environment variable).  If there is no JDK in this path, it checks for
the java executable in @code{/usr/java/bin/java}.

In case additional options need to be passed on to the JVM, the
@IndexSubentry{Options, @code{-J}}
@IndexSubentry{Java profiling, @code{-J <string>}}
@code{-J <string>} option can be used.  The string with the
option(s) has to be delimited by quotation marks in case
there is more than one argument.

The @DisplayText{} command may be used to view the performance data.  There is
no need for any special options and the same commands as previously discussed
are supported.

@IndexSubentry{Options,  @code{-viewmode}}
@IndexSubentry{Commands, @code{viewmode}}
@IndexSubentry{Java profiling, different view modes}
The @code{viewmode} command
@xref{The Viewmode}
is very useful to examine the call stacks.

For example, this is how one can see the native call stacks.  For
lay-out purposes we have restricted the list to the first five entries:

@cartouche
@smallexample
$ gprofng display text -limit 5 -viewmode machine -calltree pi.demo.er
@end smallexample
@end cartouche

@smallexample
@verbatim
Print limit set to 5
Viewmode set to machine
Functions Call Tree. Metric: Attributed Total CPU Time

Attr.      Name
Total
CPU sec.
1.381      +-<Total>
1.171        +-Pi.calculatePi(double)
0.110        +-collector_root
0.110        |  +-JavaMain
0.070        |    +-jni_CallStaticVoidMethod
@end verbatim
@end smallexample

@noindent
Note that the selection of the viewmode is echoed in the output.

@c -- A new node --------------------------------------------------------------
@node    The gprofng Tools
@chapter The gprofng Tools
@c ----------------------------------------------------------------------------

Several tools are included in @ProductName{}.  In subsequent chapters these
are discussed in detail.  Below a brief description is given, followed by an
overview of the environment variables that are supported.

@c -- A new node --------------------------------------------------------------
@node    Tools Overview
@section Tools Overview
@c ----------------------------------------------------------------------------

The following tools are supported by @ProductName{}:

@table @code

@item @CollectApp{}
@IndexSubentry{@code{gprofng}, @code{collect app}}

Collects the performance data and stores the results in an experiment
directory.  There are many options on this tool, but quite often the
defaults are sufficient.
An experiment directory is required for the subsequent analysis of
the results.

@item @DisplayText{}
@IndexSubentry{@code{gprofng}, @code{display text}}

Generates performance reports in ASCII format.  Commandline
options, and/or commands in a script file are used to control the contents
and lay-out of the generated report(s).

@item @DisplayHTML{}
@IndexSubentry{@code{gprofng}, @code{display html}}

Takes one or more experiment directories and generates a directory with
HTML files.  Starting from the index.html file, the performance data
may be examined in a browser.

@item @DisplaySRC{}
@IndexSubentry{@code{gprofng}, @code{display src}}

Displays the source code, interleaved with the disassembled instructions.

@item @Archive{}
@IndexSubentry{@code{gprofng}, @code{archive}}

Archives an experiment directory by (optionally) including source code and
object files, as well as the shared libraries that have been used.

@item @GUI{}
@IndexSubentry{@code{gprofng}, @code{display gui}}

This is an optional component that can be installed in addition to the
command line gprofng tools listed above.  It supports the graphical
analysis of one or more experiments that have been created using
@CollectApp{}.

The GUI part of @ProductName{} is a GNU project.  This is the link to the
@url{https://savannah.gnu.org/projects/gprofng-gui, gprofng GUI page}.
This page contains more information (e.g. how to clone the repo).
There is also a
@url{https://ftp.gnu.org/gnu/gprofng-gui, tar file distribution directory}
with tar files that include everything that is needed to build and install
the GUI code.  Various versions are available here.
Be aware that in order to build and use the gprofng GUI, Java needs to be
installed first.  The minimum Java version required is Java 8.

@end table

@c -- A new section -----------------------------------------------------------
@node    The gprofng.rc file with default settings
@section The gprofng.rc file with default settings
@c ----------------------------------------------------------------------------
The @file{gprofng.rc}
@cindex gprofng.rc
file is used to define default settings for the @DisplayText{}, @Archive{},
and @DisplaySRC{} tools, but the user can override these defaults through
local configuration settings when building and installing from the source
code.

There are three files that are checked when the tool starts up.  The first
file has pre-defined settings and comes with the installation, but through
a hidden file called @file{.gprofng.rc}, the user can (re)define the defaults.

These are the locations and files that are checked upon starting the above
mentioned tools:

@enumerate

@item
The system-wide filename is called @file{gprofng.rc} and is located in
the @file{/etc} subdirectory in case an RPM was used for the installation.

If @ProductName{} has been built from the source, this file is in
subdirectory @file{etc} in the top level installation directory.

@item
The user's home directory may have a hidden file called @file{.gprofng.rc}.

@item
The directory where @DisplayText{} (or @DisplaySRC{}) is invoked from, may
have a hidden file called @file{.gprofng.rc}.

@end enumerate

The settings of each file override the settings of the file(s) read before it.
Defaults in the system-wide file are overruled by the file in the user home
directory (if any) and any settings in the @file{.gprofng.rc} file in the
current directory override those.

Note that the settings in these files only affect the defaults.  Unlike
the commands used in a script file, they are not commands for the tools.

@c -- TBD indxobj_define, 
@c -- TBD object_show, 
@c -- TBD object_hide, 
@c -- TBD object_api, 

The @file{.gprofng.rc} configuration files can contain the
@command{addpath},
@command{compare}, 
@command{dthresh}, 
@command{name}, 
@command{pathmap},
@command{printmode}, 
@command{sthresh},
and
@command{viewmode} 
commands as described in this user guide.

They can also contain the following commands, @emph{which cannot be used on
either the command line, or in a script file}:

@table @code

@item dmetrics @var{metric-spec}
@IndexSubentry{Commands, @code{dmetrics}}

Specify the default metrics to be displayed or printed in the function list.
The syntax and use of the metric list is described in section
@ref{Metric Definitions}.
The order of the metric keywords in the list determines the order in which
the metrics are presented.

Default metrics for the @code{callers-callees} list are derived from the
function list default metrics by adding the corresponding attributed metric
before the first occurrence of each metric name in the list.

@item dsort @var{metric-spec}
@IndexSubentry{Commands, @code{dsort}}

Specify the default metric by which the function list is sorted.  The sort
metric is the first metric in this list that matches a metric in any loaded
experiment, subject to the following conditions:

@itemize @bullet

@item
If the entry in @var{metric-spec} has a visibility string of an exclamation
point (@samp{!}), the first metric whose name matches is used, regardless of
whether it is visible.

@item
If the entry in @var{metric-spec} has any other visibility string, the first
visible metric whose name matches is used.

@end itemize

The syntax and use of the metric list is described in section
@ref{Metric Definitions}.
The default sort metric for the @code{callers-callees} list is the attributed
metric corresponding to the default sort metric for the function list.

@item en_desc @{on | off | =@var{regex}@}
@IndexSubentry{Commands, @code{en_desc}}

Set the mode for reading descendant experiments to @samp{on} (enable all
descendants) or @samp{off} to disable all descendants.  If
@samp{=}@var{regex} is used, enable data from those experiments whose
executable name matches the regular expression.

The default setting is @samp{on} to follow all descendants.  In reading
experiments with descendants, any sub-experiments that contain little or
no performance data are ignored by @DisplayText{}.

@end table

@c -- A new section -----------------------------------------------------------
@node    Filters
@section Filters
@c ----------------------------------------------------------------------------

Various filter commands are supported by @DisplayText{}.
Thanks to the use of filters, the user can zoom in on a certain area of
interest.  With filters, it is possible to select one or more threads to
focus on, define a window in time, select specific call stacks, etc.
@IndexSubentry{Filters, Intro}

While already powerful by themselves, filters may be combined to further
narrow down the view into the data.

@IndexSubentry{Filters, Persistence}
It is important to note that filters are @emph{persistent}.  A filter is
active until it is reset.  This means that successive filter commands
increasingly narrow down the view until one or more are reset.

@noindent
An example is the following:

@cartouche
@smallexample
$ gprofng display text -thread_select 1 -functions \
                       -cpu_select 2 -functions @dots{}
@end smallexample
@end cartouche

This command selects thread 1 and requests the function view for this thread.
The third (@command{cpu_select 2}) command @emph{adds} the
constraint that only the events on CPU 2 are to be selected.  This means
that the next function view selects events that were executed by thread 1 and
have been running on CPU 2.

@noindent
In contrast with this single command line, the two commands below look similar,
but behave very differently:

@cartouche
@smallexample
$ gprofng display text -thread_select 1 -functions @dots{}
$ gprofng display text -cpu_select 2 -functions @dots{}
@end smallexample
@end cartouche

The first command displays the function view for thread 1.  The second
command shows the function view for CPU 2 for @emph{all} threads that have
been running on this CPU.

As the following example demonstrates, things get a little more tricky in
case a script file is used.  Consider the following script file:

@smallexample
@verbatim
thread_select 1
functions
cpu_select 2
functions
@end verbatim
@end smallexample

This script file displays the function view for thread 1 first.  This is
followed by those functions that were executed by thread 1 @emph{and} have
been run on CPU 2.

If however, the script should behave like the two command line invocations
shown above, the thread selection filter needs to be reset before CPU 2 is
selected:

@smallexample
@verbatim
thread_select 1
functions
# Reset the thread selection filter:
thread_select all
cpu_select 2
functions
@end verbatim
@end smallexample

In general, filters behave differently than commands or options.  In
particular there may be an interaction between different filter definitions.

For example, as explained above, in the first script file the
@command{thread_select} and @command{cpu_select} commands interact.

For a list of all the predefined filters see @ref{Predefined Filters}.

@c -- A new section -----------------------------------------------------------
@node    Supported Environment Variables
@section Supported Environment Variables
@c ----------------------------------------------------------------------------

Various environment variables are supported.  We refer to the man page for
gprofng(1) for an overview and description
(@xref{Man page for @command{gprofng}}).

@c -- A new chapter -----------------------------------------------------------
@node    Performance Data Collection
@chapter Performance Data Collection
@c ----------------------------------------------------------------------------

The @CollectApp{} command is used to gather the application performance data
while the application executes.
At regular intervals, program execution is halted and the required data is
recorded.
@cindex Experiment directory
An experiment directory is created when the tool starts.  This directory is
used to store the relevant information and forms the basis for a subsequent
analysis with one of the viewing tools.

@c -- A new section -----------------------------------------------------------
@node    The @command{gprofng collect app} Tool
@section The @command{gprofng collect app} Tool
@c ----------------------------------------------------------------------------

This is the command to collect the performance information for the target
application.  The usage is as follows:

@cartouche
@smallexample
$ gprofng collect app [OPTION(S)] TARGET [TARGET_ARGUMENTS]
@end smallexample
@end cartouche

@noindent
Options to the command are passed in first.  This is followed by the name of
the target, which is typically a binary executable or a script, followed by
any options that may be required by the target.

@c -- A new section -----------------------------------------------------------
@node    View the Performance Information
@chapter View the Performance Information
@c ----------------------------------------------------------------------------
Various tools to view the performance data stored in one or more experiment
directories are available.  In this chapter, these will all be covered in
detail.

@c -- A new section -----------------------------------------------------------
@node    The @command{gprofng display text} Tool
@section The @command{gprofng display text} Tool
@c ----------------------------------------------------------------------------

This tool displays the performance information in ASCII format.  It supports
a variety of views into the data recorded.
These views can be specified in two ways and both may be used simultaneously:

@itemize @bullet

@item
Command line options start with a dash (@samp{-}) symbol and may take an
argument.

@item
Options may also be included in a file, the ``script file''.  In this case,
the dash symbol should @emph{not} be included.  Multiple script files can
be used on the same command line.

@end itemize

While they may appear as an option, they are really commands and this is
why they will be referred to as @emph{commands}
@cindex Commands
in the documentation.

As a general rule, @emph{the order of options matters} and if the same option,
or command, occurs multiple times, the rightmost setting is selected.

@c -- A new sub section -------------------------------------------------------
@node       The @code{gprofng display text} Commands
@subsection The @code{gprofng display text} Commands
@c ----------------------------------------------------------------------------

The most commonly used commands are documented in the man page for this tool
(@xref{Man page for @command{gprofng display text}}).  In this section we list
and describe all other commands that are supported.

@c -- A new sub subsection ----------------------------------------------------
@node                Commands that List Experiment Details
@unnumberedsubsubsec Commands that List Experiment Details
@c ----------------------------------------------------------------------------

@table @code

@item experiment_ids
@ifclear man
@IndexSubentry{Options,  @code{-experiment_ids}}
@IndexSubentry{Commands, @code{experiment_ids}}
@end ifclear

For each experiment that has been loaded, show the totals of the metrics
recorded, plus some other operational characteristics like the name of
the executable, PID, etc.  The top line contains the accumulated totals
for the metrics.

@item experiment_list
@ifclear man
@IndexSubentry{Options,  @code{-experiment_list}}
@IndexSubentry{Commands, @code{experiment_list}}
@end ifclear

Display the list of experiments that are loaded.  Each experiment is listed
with an index, which is used when selecting samples, threads, or LWPs, and
a process id (PID), which can be used for advanced filtering.

@item cpu_list
@IndexSubentry{Options,  @code{-cpu_list}}
@IndexSubentry{Commands, @code{cpu_list}}

Display the total number of CPUs that have been used during the experiment(s).

@item cpus
@IndexSubentry{Options,  @code{-cpus}}
@IndexSubentry{Commands, @code{cpus}}

Show a list of CPUs that were used by the application, along with the metrics
that have been recorded.  The CPUs are represented by a CPU number and show
the Total CPU time by default.

Note that since the data is sorted with respect to the default metric, it may
be useful to use the @command{sort name} command to show the list sorted with
respect to the CPU id.

@item GCEvents
@IndexSubentry{Options,  @code{-GCEvents}}
@IndexSubentry{Commands, @code{GCEvents}}

This commands is for Java applications only.  It shows any Garbage Collection
(GC) events that have occurred while the application was executing.

@item lwp_list
@IndexSubentry{Options,  @code{-lwp_list}}
@IndexSubentry{Commands, @code{lwp_list}}

Displays the list of LWPs processed during the experiment(s).

@item processes
@IndexSubentry{Options,  @code{-processes}}
@IndexSubentry{Commands, @code{processes}}

For each experiment that has been loaded, this command displays a list of
processes that were created by the application, along with their metrics.
The processes are represented by process ID (PID) numbers and show the
Total CPU time metric by default.  If additional metrics are recorded in
an experiment, these are shown as well.

@item samples
@IndexSubentry{Options,  @code{-samples}}
@IndexSubentry{Commands, @code{samples}}

Display a list of sample points and their metrics, which reflect the
microstates recorded at each sample point in the loaded experiment.
The samples are represented by sample numbers and show the Total CPU time
by default.  Other metrics might also be displayed if enabled.

@item sample_list
@IndexSubentry{Options,  @code{-sample_list}}
@IndexSubentry{Commands, @code{sample_list}}

For each experiment loaded, display the list of samples currently selected.

@item seconds
@IndexSubentry{Options,  @code{-seconds}}
@IndexSubentry{Commands, @code{seconds}}

Show each second of the profiling run that was captured in the experiment,
along with the metrics collected in that second.  The seconds view differs
from the samples view in that it shows periodic samples that occur every
second beginning at 0 and the interval cannot be changed.

The seconds view lists the seconds of execution with the Total CPU time by
default.  Other metrics might also be displayed if the metrics are present
in the loaded experiments.

@item threads
@IndexSubentry{Options,  @code{-threads}}
@IndexSubentry{Commands, @code{threads}}

Show a list of threads and their metrics.  The threads are represented
by a process and thread pair and show the Total CPU time by default.
Other metrics might also be displayed by default if the metrics are
present in the loaded experiment.

@item thread_list
@IndexSubentry{Options,  @code{-thread_list}}
@IndexSubentry{Commands, @code{thread_list}}

Display the list of threads currently selected for the analysis.

@end table

@noindent
@emph{The commands below are for use in scripts and interactive mode only.
They are not allowed on the command line.}

@table @code

@item add_exp @var{exp-name}
@IndexSubentry{Commands, @code{add_exp}}

Add the named experiment to the current session.

@item drop_exp @var{exp-name}
@IndexSubentry{Commands, @code{drop_exp}}

Drop the named experiment from the current session.

@item open_exp @var{exp-name}
@IndexSubentry{Commands, @code{open_exp}}

Drop all loaded experiments from the session, and then load the named
experiment.

@end table

@c -- A new sub subsection ----------------------------------------------------
@node                Commands that Affect Listings and Output
@unnumberedsubsubsec Commands that Affect Listings and Output
@c ----------------------------------------------------------------------------

@table @code

@item dthresh @var{value}
@IndexSubentry{Options,  @code{-dthresh}}
@IndexSubentry{Commands, @code{dthresh}}

Specify the threshold percentage for highlighting metrics in the annotated
disassembly code.  If the value of any metric is equal to or greater than
@var{value} as a percentage of the maximum value of that metric for any
instruction line in the file, the line on which the metrics occur has a
@samp{##} marker inserted at the beginning of the line.  The default is 75.

@item printmode @{text | html | @var{single-char}@}
@IndexSubentry{Options,  @code{-printmode}}
@IndexSubentry{Commands, @code{printmode}}

Set the print mode.  If the keyword is @code{text}, printing will be done in
tabular form using plain text.  In case the @code{html} keyword is selected,
the output is formatted as an HTML table.

Alternatively, @var{single-char} may be used in a delimiter separated list,
with the single character @var{single-char} as the delimiter.

The printmode setting is used only for those commands that generate tables,
such as @command{functions}.  The setting is ignored for other printing
commands, including those showing source and disassembly listings.

@item sthresh @var{value}
@IndexSubentry{Options,  @code{-sthresh}}
@IndexSubentry{Commands, @code{sthresh}}

Specify the threshold percentage for highlighting metrics in the annotated
source code.  If the value of any metric is equal to or greater than
@var{value} (as a percentage) of the maximum value of that metric for any
source line in the file, the line on which the metrics occur has a @samp{##}
marker inserted at the beginning of the line.  The default is 75.

@end table

@c -- A new sub subsection ----------------------------------------------------
@node                Predefined Filters
@unnumberedsubsubsec Predefined Filters
@c ----------------------------------------------------------------------------

The filters below use a list, the selection list, to define a sequence of
numbers. @xref{The Selection List}.
Note that this selection is persistent, but the filter can be reset by using
@samp{all} as the @var{selection-list}.

@table @code

@item cpu_select @var{selection-list}
@IndexSubentry{Options,  @code{-cpu_select}}
@IndexSubentry{Commands, @code{cpu_select}}

Select the CPU ids specified in the @var{selection-list}.

@item lwp_select @var{selection-list}
@IndexSubentry{Options,  @code{-lwp_select}}
@IndexSubentry{Commands, @code{lwp_select}}

Select the LWPs specified in the @var{selection-list}.

@item sample_select @var{selection-list}
@IndexSubentry{Options,  @code{-sample-select}}
@IndexSubentry{Commands, @code{sample-select}}

@item thread_select @var{selection-list}
@IndexSubentry{Options,  @code{-thread_select}}
@IndexSubentry{Commands, @code{thread_select}}

Select a series of threads, or just one, to be used in subsequent views.
The @var{selection-list} consists of a sequence of comma separated numbers.
This may include a range of the form @samp{n-m}.

@end table


@c -- A new sub subsection ----------------------------------------------------
@node                Commands to Set and Change Search Paths
@unnumberedsubsubsec Commands to Set and Change Search Paths
@c ----------------------------------------------------------------------------

@table @code

@item addpath @var{path-list}
@IndexSubentry{Options,  @code{-addpath}}
@IndexSubentry{Commands, @code{addpath}}

Append @var{path-list} to the current setpath settings.  Note that multiple
@command{addpath} commands can be used in @file{.gprofng.rc} files, and will
be concatenated.

@item pathmap @var{old-prefix} @var{new-prefix}
@IndexSubentry{Options,  @code{-pathmap}}
@IndexSubentry{Commands, @code{pathmap}}

If a file cannot be found using the path list set by @command{addpath}, or
the @command{setpath} command, one or more path remappings may be set with the
@command{pathmap} command.

With path mapping, the user can specify how to replace the leading component
in a full path by a different string.

With this command, any path name for a source file, object file, or shared
object that begins with the prefix specified with @var{old-prefix}, the
old prefix is replaced by the prefix specified with @var{new-prefix}.
The resulting path is used to find the file.

For example, if a source file located in directory @file{/tmp}
is shown in the @DisplayText{} output, but should instead be taken from
@file{/home/demo}, the following @file{pathmap} command redefines the
path:

@smallexample
$ gprofng diplay text -pathmap /tmp /home/demo -source ...
@end smallexample

Note that multiple @command{pathmap} commands can be supplied, and each is
tried until the file is found.

@item setpath @var{path-list}
@IndexSubentry{Options,  @code{-setpath}}
@IndexSubentry{Commands, @code{setpath}}

Set the path used to find source and object files.  The path is defined
through the @var{path-list} keyword.  It is a colon separated list of
directories, jar files, or zip files.
If any directory has a colon character in it, escape it with a
backslash (@samp{\}).

The special directory name @code{$expts}, refers
to the set of current experiments in the order in which they were loaded.
You can abbreviate it with a single @samp{$} character.

The default path is @samp{$expts:..} which is the directories of the
loaded experiments and the current working directory.

Use @command{setpath} with no argument to display the current path.

Note that @command{setpath} commands @emph{are not allowed .gprofng.rc
configuration files}.

@end table

@c -- A new subsection --------------------------------------------------------
@c -- TBD @node       Usage examples for @code{gprofng display text}
@c -- TBD @subsection Usage examples for @code{gprofng display text}
@c ----------------------------------------------------------------------------

@c -- TBD In this section we present usage examples.

@c -- A new chapter -----------------------------------------------------------
@c  TBD @node    The @code{gprofng display html} Tool
@c  TBD @section The @code{gprofng display html} Tool
@c ----------------------------------------------------------------------------
@c  TBD The options are documented in the man page for this tool. In this section we
@c  TBD present usage examples.

@c -- A new chapter -----------------------------------------------------------
@c  TBD @node    Display Source Code
@c  TBD @chapter Display Source Code
@c ----------------------------------------------------------------------------
@c  TBD The options are documented in the man page for this tool. In this section we
@c  TBD present usage examples.


@c -- A new chapter -----------------------------------------------------------
@c  TBD @node    Archive Experiment Data
@c  TBD @chapter Archive Experiment Data
@c ----------------------------------------------------------------------------
@c  TBD The options are documented in the man page for this tool. In this section we
@c  TBD present usage examples.

@c -- A new chapter -----------------------------------------------------------
@node    Terminology
@chapter Terminology
@c ----------------------------------------------------------------------------

Throughout this manual, certain terminology specific to profiling tools,
or @ToolName{}, or even to this document only, is used.  In this chapter
this terminology is explained in detail.

@menu
* The Program Counter::                    What is a Program Counter?
* Inclusive and Exclusive Metrics::        An explanation of inclusive and exclusive metrics.
* Metric Definitions::                     Definitions associated with metrics.
* The Viewmode::                           Select the way call stacks are presented.
* The Selection List::                     How to define a selection.
* Load Objects and Functions::             The components in an application.
* The Concept of a CPU in gprofng::        The definition of a CPU.
* Hardware Event Counters Explained::      What are event counters?
* apath::                                  Our generic definition of a path.
@end menu

@c ----------------------------------------------------------------------------
@node    The Program Counter
@section The Program Counter
@c ----------------------------------------------------------------------------

@cindex PC
@cindex Program Counter
The @emph{Program Counter}, or PC for short, keeps track where program
execution is.  The address of the next instruction to be executed is stored
in a special purpose register in the processor, or core.

@cindex Instruction pointer
The PC is sometimes also referred to as the @emph{instruction pointer}, but
we will use Program Counter or PC throughout this document.

@c ----------------------------------------------------------------------------
@node    Inclusive and Exclusive Metrics
@section Inclusive and Exclusive Metrics
@c ----------------------------------------------------------------------------

In the remainder, these two concepts occur quite often and for lack of a better
place, they are explained here.

@cindex Inclusive metric
The @emph{inclusive} value for a metric includes all values that are part of
the dynamic extent of the target function.  For example if function @code{A}
calls functions @code{B} and @code{C}, the inclusive CPU time for @code{A}
includes the CPU time spent in @code{B} and @code{C}.

@cindex Exclusive metric
In contrast with this, the @emph{exclusive} value for a metric is computed
by excluding the metric values used by other functions called.  In our
imaginary example, the exclusive CPU time for function @code{A} is the
time spent outside calling functions @code{B} and @code{C}.

@cindex Leaf function
In case of a @emph{leaf function}, the inclusive and exclusive values for the
metric are the same since by definition, it is not calling any other
function(s).

Why do we use these two different values? The inclusive metric shows the most
expensive path, in terms of this metric, in the application.  For example, if
the metric is cache misses, the function with the highest inclusive metric
tells you where most of the cache misses come from.

Within this branch of the application, the exclusive metric points to the
functions that contribute and help to identify which part(s) to consider
for further analysis.

@c ----------------------------------------------------------------------------
@node    Metric Definitions
@section Metric Definitions
@c ----------------------------------------------------------------------------
The metrics displayed in the various views are highly customizable.  In this
section it is explained how to construct the metrics definition(s).

@IndexSubentry{Options,  @code{-metrics}}
@IndexSubentry{Commands, @code{metrics}}
The @command{metrics} command takes a colon (@samp{:}) separated list, where
each item in the list consists of the following three fields:
@var{<flavor>}@var{<visibility>}@var{<metric-name>}.

@cindex Flavor field
@cindex Visibility field
@cindex Metric name field
@IndexSubentry{Metrics, Flavor field}
@IndexSubentry{Metrics, Visibility field}
@IndexSubentry{Metrics, Metric name field}
The @var{<flavor>} field is either @samp{e} for ``exclusive'', and/or
@samp{i} for ``inclusive''.  The @var{<metric-name>} field is the name of
the metric and the @var{<visibility>} field consists of one ore more characters
from the following table:

@table @code

@item .
Show the metric as time.  This applies to timing metrics and hardware event
counters that measure cycles.  Interpret as @samp{+} for other metrics.

@item %
Show the metric as a percentage of the total value for this metric.

@item +
Show the metric as an absolute value.  For hardware event counters this is
the event count.  Interpret as @samp{.} for timing metrics.

@item !
Do not show any metric value.  Cannot be used with other visibility characters.
This visibility is meant to be used in a @command{dmetrics} command to set
default metrics that override the built-in visibility defaults
for each type of metric.

@end table

Both the @var{<flavor>} and @var{<visibility>} strings may have more than one
character.  If both strings have more than one character, the @var{<flavor>}
string is expanded first.  For example, @code{ie.%user} is first expanded to
@code{i.%user:e.%user}, which is then expanded into
@code{i.user:i%user:e.user:e%user}.

@c ----------------------------------------------------------------------------
@node    The Viewmode
@section The Viewmode

@cindex Viewmode
@IndexSubentry{Options,  @code{-viewmode}}
@IndexSubentry{Commands, @code{viewmode}}

There are different ways to view a call stack in Java.  In @ToolName{}, this
is called the @emph{viewmode} and the setting is controlled through a command
with the same name.

The @code{viewmode} command takes one of the following keywords:

@table @code

@item user
This is the default and shows the Java call stacks for Java threads.
No call stacks for any housekeeping threads are shown.  The function
list contains a function
@IndexSubentry{Java profiling, @code{<JVM-System>}}
@code{<JVM-System>} that represents the aggregated time from non-Java
threads.
When the JVM software does not report a Java call stack, time is reported
against the function
@IndexSubentry{Java profiling, @code{<no Java callstack recorded>}}
@code{<no Java callstack recorded>}.

@item expert
Show the Java call stacks for Java threads when the Java code from the
user is executed and machine call stacks when JVM code is executed, or
when the JVM software does not report a Java call stack.
Show the machine call stacks for housekeeping threads.

@item machine
Show the actual native call stacks for all threads.

@end table

@c ----------------------------------------------------------------------------
@node    The Selection List
@section The Selection List
@c ----------------------------------------------------------------------------

@cindex Selection list
@cindex List specification
Several commands allow the user to specify a sequence of numbers called the
@emph{selection list}.  Such a list may for example be used to select specific
threads from all the threads that have been used when conducting the
experiment(s).

A selection list (or ``list'' in the remainder of this section) can be a
single number, a contiguous range of numbers with the start and end numbers
separated by a hyphen (@samp{-}), a comma-separated list of numbers and
ranges, or the @code{all} keyword that resets the filter.
@IndexSubentry{Filters, Reset to default}
Lists must not contain spaces.

Each list can optionally be preceded by an experiment list with a similar
format, separated from the list by a colon (:).
If no experiment list is included, the list applies to all experiments.

Multiple lists can be concatenated by separating the individual lists
by a plus sign.

These are some examples of various filters using a list:

@table @code

@item thread_select 1
Select thread 1 from all experiments.

@item thread_select all:1
Select thread 1 from all experiments.

@item thread_select 1:all
Select all the threads from the first experiment loaded.

@item thread_select 1:2+3:4
Select thread 2 from experiment 1 and thread 4 from experiment 3.

@item cpu_select all:1,3,5
Selects cores 1, 3, and 5 from all experiments.

@item cpu_select 1,2:all
Select all cores from experiments 1 and 2.

@end table

Recall that there are several list commands that show the mapping between the
numbers and the targets.

@IndexSubentry{Options, @code{-experiment_list}}
@IndexSubentry{Commands, @code{experiment_list}}
For example, the @command{experiment_list} command shows the name(s) of the
experiment(s) loaded and the associated number.  In this example it is used
to get this information for a range of experiments:

@cartouche
@smallexample
$ gprofng display text -experiment_list mxv.?.thr.er
@end smallexample
@end cartouche

@noindent
This is the output, showing for each experiment the ID, the PID, and the name:

@smallexample
@verbatim
ID Sel     PID Experiment
== === ======= ============
 1 yes 2750071 mxv.1.thr.er
 2 yes 1339450 mxv.2.thr.er
 3 yes 3579561 mxv.4.thr.er
@end verbatim
@end smallexample

@c ----------------------------------------------------------------------------
@node    Load Objects and Functions
@section Load Objects and Functions
@c ----------------------------------------------------------------------------

An application consists of various components.  The source code files are
compiled into object files.  These are then glued together at link time to form
the executable.
During execution, the program may also dynamically load objects.

@cindex Load object
A @emph{load object} is defined to be an executable, or shared object.  A
shared library is an example of a load object in @ToolName{}.

Each load object, contains a text section with the instructions generated by
the compiler, a data section for data, and various symbol tables.
All load objects must contain an
@cindex ELF
ELF
symbol table, which gives the names and addresses of all the globally known
functions in that object.

Load objects compiled with the -g option contain additional symbolic
information that can augment the ELF symbol table and provide information
about functions that are not global, additional information about object
modules from which the functions came, and line number information relating
addresses to source lines.

The term
@cindex Function
@emph{function}
is used to describe a set of instructions that represent a high-level operation
described in the source code.  The term also covers methods as used in C++
and in the Java programming language.

In the @ToolName{} context, functions are provided in source code format.
Normally their names appear in the symbol table representing a set of
addresses.
@cindex Program Counter
@cindex PC
If the Program Counter (PC) is within that set, the program is executing within
that function.

In principle, any address within the text segment of a load object can be
mapped to a function.  Exactly the same mapping is used for the leaf PC and
all the other PCs on the call stack.

Most of the functions correspond directly to the source model of the program,
but there are exceptions.  This topic is however outside of the scope of this
guide.

@c ----------------------------------------------------------------------------
@node    The Concept of a CPU in gprofng
@section The Concept of a CPU in gprofng
@c ----------------------------------------------------------------------------

@cindex CPU
In @ProductName{}, there is the concept of a CPU.  Admittedly, this is not the
best word to describe what is meant here and may be replaced in the future.

The word CPU is used in many of the displays.
In the context of @ProductName{}, it is meant to denote a part of the
processor that is capable of executing instructions and with its own state,
like the program counter.

For example, on a contemporary processor, a CPU could be a core.  In case
hardware threads are supported within a core, a CPU is one of those
hardware threads.

To see which CPUs have been used in the experiment, use the @command{cpu}
command in @DisplayText{}.

@c ----------------------------------------------------------------------------
@node    Hardware Event Counters Explained
@section Hardware Event Counters Explained
@c ----------------------------------------------------------------------------

@IndexSubentry{Hardware event counters, description}
For quite a number of years now, many microprocessors have supported hardware
event counters.

On the hardware side, this means that in the processor there are one or more
registers dedicated to count certain activities, or ``events''.
Examples of such events are the number of instructions executed, or the
number of cache misses at level 2 in the memory hierarchy.

While there is a limited set of such registers, the user can map events onto
them.  In case more than one register is available, this allows for the
simultaenous measurement of various events.

A simple, yet powerful, example is to simultaneously count the number of CPU
cycles and the number of instructions excuted.  These two numbers can then be
used to compute the
@cindex IPC
@emph{IPC} value.  IPC stands for ``Instructions Per Clockcycle'' and each
processor has an architecturally defined maximum.  For example, if this
maximum number is 2, it means the processor is capable of executing two
instructions every clock cycle.

Whether this is actually achieved, depends on several factors, including the
instruction characteristics.
However, in case the IPC value is well below this maximum in a time critical
part of the application and this cannot be easily explained, further
investigation is probably warranted.

@cindex CPI
A related metric is called @emph{CPI}, or ``Clockcycles Per Instruction''.
It is the inverse of the CPI and can be compared against the theoretical
value(s) of the target instruction(s).  A significant difference may point
at a bottleneck.

One thing to keep in mind is that the value returned by a counter can either
be the number of times the event occured, or a CPU cycle count.  In case of
the latter it is possible to convert this number to time.

@IndexSubentry{Hardware event counters, variable CPU frequency}
This is often easier to interpret than a simple count, but there is one
caveat to keep in mind.  The CPU frequency may not have been constant while
the experimen was recorded and this impacts the time reported.

These event counters, or ``counters'' for short, provide great insight into
what happens deep inside the processor.  In case higher level information does
not provide the insight needed, the counters provide the information to get
to the bottom of a performance problem.

There are some things to consider though.

@itemize @bullet

@item
The event definitions and names vary across processors and it may even happen
that some events change with an update.
Unfortunately and this is luckily rare, there are sometimes bugs causing the
wrong count to be returned.

@IndexSubentry{Hardware event counters, alias name}
In @ToolName{}, some of the processor specific event names have an alias
name.  For example @code{insts} measures the instructions executed.
These aliases not only makes it easier to identify the functionality, but also
provide portability of certain events across processors.

@item
Another complexity is that there are typically many events one can monitor.
There may up to hundreds of events available and it could require several
experiments to zoom in on the root cause of a performance problem.

@item
There may be restrictions regarding the mapping of event(s) onto the
counters.  For example, certain events may be restricted to specific
counters only.  As a result, one may have to conduct additional experiments
to cover all the events of interest.

@item
The names of the events may also not be easy to interpret.  In such cases,
the description can be found in the architecture manual for the processor.

@end itemize

Despite these drawbacks, hardware event counters are extremely useful and
may even turn out to be indispensable.

@c ----------------------------------------------------------------------------
@node    apath
@section What is <apath>?
@c ----------------------------------------------------------------------------

In most cases, @ToolName{} shows the absolute pathnames of directories.  These
tend to be rather long, causing display issues in this document.

Instead of wrapping these long pathnames over multiple lines, we decided to
represent them by the @code{<apath>} symbol, which stands for ``an absolute
pathname''.

Note that different occurrences of @code{<apath>} may represent different
absolute pathnames.

@c -- A new node --------------------------------------------------------------
@node    Other Document Formats
@chapter Other Document Formats
@c ----------------------------------------------------------------------------

@emph{This chapter is applicable when building gprofng from the
binutils source.}

This document is written in Texinfo and the source text is made available as
part of the binutils distribution.  The file name is @code{gprofng.texi} and
can be found in subdirectory @code{gprofng/doc} of the top level binutils
directory.

The default installation procedure creates a file in the @code{info} format and
stores it in the documentation section of binutils.
This source file can however also be used to generate the document in the
@code{html} and @code{pdf} formats.  These may be easier to read and search.

To generate this documentation file in a different format, go to the directory
that was used to build the tools.  The make file to build the other formats is
in the @code{gprofng/doc} subdirectory.

For example, if you have set the build directory to be @var{<my-build-dir>},
go to subdirectory @var{<my-build-dir>/gprofng/doc}.

This subdirectory has a single file called @file{Makefile} that can be used to
build the documentation in various formats.  We recommend to use these
commands.

There are four commands to generate the documentation in the @code{html} or
@code{pdf} format.  It is assumed that you are in directory @code{gprofng/doc}
under the main directory @var{<my-build-dir>}.

@table @code

@item make html
Create the html file in the current directory.

@item make pdf
Create the pdf file in the current directory.

@item make install-html
Create and install the html file in the binutils documentation directory.

@item make install-pdf
Create and install the pdf file in the binutils documentation directory.

@end table

For example, to install this document in the binutils documentation directory,
the commands below may be executed.  In this notation, @var{<format>}
is one of @code{html}, or @code{pdf}:

@smallexample
@verbatim
$ cd <my-build-dir>/gprofng/doc
$ make install-<format>
@end verbatim
@end smallexample

The binutils installation directory is either the default @code{/usr/local} or
the one that has been set with the @code{--prefix} option as part of the
@code{configure} command.  In this example we symbolize this location with
@code{<install>}.

The documentation directory is @code{<install>/share/doc/gprofng} in case
@code{html} or @code{pdf} is selected and @code{<install>/share/info} for the
file in the @code{info} format.

@noindent
Some things to note:

@itemize

@item
For the @code{pdf} file to be generated, the @code{texi2dvi} tool is required.
@cindex texi2dvi
It is for example available as part of the @code{texinfo-tex} package.

@item
Instead of generating a single file in the @code{html} format, it is also
possible to create a directory with individual files for the various chapters.
To do so, remove the use of @code{--no-split} in variable @code{MAKEINFOHTML}
in the make file in the @code{<my-build-dir/gprofng/doc} directory.

@end itemize

@c -- An appendix -------------------------------------------------------------
@node     The gprofng Man Pages
@appendix The gprofng Man Pages
@c ----------------------------------------------------------------------------

In this appendix the man pages for the various @ProductName{} tools are listed.

@c -- A new node --------------------------------------------------------------
@c  @node    gprofng driver
@node    Man page for @command{gprofng}
@section Man page for @command{gprofng}
@c ----------------------------------------------------------------------------

@include gprofng.texi

@c -- A new node --------------------------------------------------------------
@page
@node    Man page for @command{gprofng collect app}
@section Man page for @command{gprofng collect app}
@c ----------------------------------------------------------------------------

@include gprofng-collect-app.texi

@c -- A new node --------------------------------------------------------------
@page
@node    Man page for @command{gprofng display text}
@section Man page for @command{gprofng display text}
@c ----------------------------------------------------------------------------

@include gprofng-display-text.texi

@c -- A new node --------------------------------------------------------------
@page
@node    Man page for @command{gprofng display html}
@section Man page for @command{gprofng display html}
@c ----------------------------------------------------------------------------

@include gprofng-display-html.texi

@c -- A new node --------------------------------------------------------------
@page
@node    Man page for @command{gprofng display src}
@section Man page for @command{gprofng display src}
@c ----------------------------------------------------------------------------

@include gprofng-display-src.texi

@c -- A new node --------------------------------------------------------------
@page
@node    Man page for @command{gprofng archive}
@section Man page for @command{gprofng archive}
@c ----------------------------------------------------------------------------

@include gprofng-archive.texi

@ifnothtml
@node       Index
@unnumbered Index
@printindex cp
@end ifnothtml

@bye