From 336ab2d51dfdd5ca09c2a9c506453db4fe653584 Mon Sep 17 00:00:00 2001
From: Alexandre Ganea <alexandre.ganea@ubisoft.com>
Date: Wed, 13 Jan 2021 20:59:31 -0500
Subject: [Support] On Windows, take the affinity mask into account

The number of hardware threads available to a ThreadPool can be limited if setting an affinity mask.
For example:

> start /B /AFFINITY 0xF lld-link.exe ...

Would let LLD only use 4 hyper-threads.

Previously, there was an outstanding issue on Windows Server 2019 on dual-CPU machines, which was preventing from using both CPU sockets. In normal conditions, when no affinity mask was set, ProcessorGroup::AllThreads was different from ProcessorGroup::UsableThreads. The previous code in llvm/lib/Support/Windows/Threading.inc L201 was improperly assuming those two values to be equal, and consequently was limiting the execution to only one CPU socket.

Differential Revision: https://reviews.llvm.org/D92419
---
 llvm/lib/Support/Program.cpp | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

(limited to 'llvm/lib/Support/Program.cpp')

diff --git a/llvm/lib/Support/Program.cpp b/llvm/lib/Support/Program.cpp
index 5294f65..c7a5964 100644
--- a/llvm/lib/Support/Program.cpp
+++ b/llvm/lib/Support/Program.cpp
@@ -26,17 +26,20 @@ using namespace sys;
 static bool Execute(ProcessInfo &PI, StringRef Program,
                     ArrayRef<StringRef> Args, Optional<ArrayRef<StringRef>> Env,
                     ArrayRef<Optional<StringRef>> Redirects,
-                    unsigned MemoryLimit, std::string *ErrMsg);
+                    unsigned MemoryLimit, std::string *ErrMsg,
+                    BitVector *AffinityMask);
 
 int sys::ExecuteAndWait(StringRef Program, ArrayRef<StringRef> Args,
                         Optional<ArrayRef<StringRef>> Env,
                         ArrayRef<Optional<StringRef>> Redirects,
                         unsigned SecondsToWait, unsigned MemoryLimit,
                         std::string *ErrMsg, bool *ExecutionFailed,
-                        Optional<ProcessStatistics> *ProcStat) {
+                        Optional<ProcessStatistics> *ProcStat,
+                        BitVector *AffinityMask) {
   assert(Redirects.empty() || Redirects.size() == 3);
   ProcessInfo PI;
-  if (Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg)) {
+  if (Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg,
+              AffinityMask)) {
     if (ExecutionFailed)
       *ExecutionFailed = false;
     ProcessInfo Result =
@@ -55,12 +58,13 @@ ProcessInfo sys::ExecuteNoWait(StringRef Program, ArrayRef<StringRef> Args,
                                Optional<ArrayRef<StringRef>> Env,
                                ArrayRef<Optional<StringRef>> Redirects,
                                unsigned MemoryLimit, std::string *ErrMsg,
-                               bool *ExecutionFailed) {
+                               bool *ExecutionFailed, BitVector *AffinityMask) {
   assert(Redirects.empty() || Redirects.size() == 3);
   ProcessInfo PI;
   if (ExecutionFailed)
     *ExecutionFailed = false;
-  if (!Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg))
+  if (!Execute(PI, Program, Args, Env, Redirects, MemoryLimit, ErrMsg,
+               AffinityMask))
     if (ExecutionFailed)
       *ExecutionFailed = true;
 
-- 
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