tunables: Add IFUNC selection and cache sizes

The current IFUNC selection is based on microbenchmarks in glibc.  It
should give the best performance for most workloads.  But other choices
may have better performance for a particular workload or on the hardware
which wasn't available at the selection was made.  The environment
variable, GLIBC_TUNABLES=glibc.tune.ifunc=-xxx,yyy,-zzz...., can be used
to enable CPU/ARCH feature yyy, disable CPU/ARCH feature yyy and zzz,
where the feature name is case-sensitive and has to match the ones in
cpu-features.h.  It can be used by glibc developers to override the
IFUNC selection to tune for a new processor or improve performance for
a particular workload.  It isn't intended for normal end users.

NOTE: the IFUNC selection may change over time.  Please check all
multiarch implementations when experimenting.

Also, GLIBC_TUNABLES=glibc.tune.x86_non_temporal_threshold=NUMBER is
provided to set threshold to use non temporal store to NUMBER,
GLIBC_TUNABLES=glibc.tune.x86_data_cache_size=NUMBER to set data cache
size, GLIBC_TUNABLES=glibc.tune.x86_shared_cache_size=NUMBER to set
shared cache size.

	* elf/dl-tunables.list (tune): Add ifunc,
	x86_non_temporal_threshold,
	x86_data_cache_size and x86_shared_cache_size.
	* manual/tunables.texi: Document glibc.tune.ifunc,
	glibc.tune.x86_data_cache_size, glibc.tune.x86_shared_cache_size
	and glibc.tune.x86_non_temporal_threshold.
	* sysdeps/unix/sysv/linux/x86/dl-sysdep.c: New file.
	* sysdeps/x86/cpu-tunables.c: Likewise.
	* sysdeps/x86/cacheinfo.c
	(init_cacheinfo): Check and get data cache size, shared cache
	size and non temporal threshold from cpu_features.
	* sysdeps/x86/cpu-features.c [HAVE_TUNABLES] (TUNABLE_NAMESPACE):
	New.
	[HAVE_TUNABLES] Include <unistd.h>.
	[HAVE_TUNABLES] Include <elf/dl-tunables.h>.
	[HAVE_TUNABLES] (TUNABLE_CALLBACK (set_ifunc)): Likewise.
	[HAVE_TUNABLES] (init_cpu_features): Use TUNABLE_GET to set
	IFUNC selection, data cache size, shared cache size and non
	temporal threshold.
	* sysdeps/x86/cpu-features.h (cpu_features): Add data_cache_size,
	shared_cache_size and non_temporal_threshold.

1 files changed, 36 insertions, 0 deletions

diff --git a/manual/tunables.texi b/manual/tunables.texi
index c9a4cb7..3263f94 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -198,6 +198,14 @@ is 8 times the number of cores online.
 @cindex hardware capability tunables
 @cindex hwcap tunables
 @cindex tunables, hwcap
+@cindex ifunc tunables
+@cindex tunables, ifunc
+@cindex data_cache_size tunables
+@cindex tunables, data_cache_size
+@cindex shared_cache_size tunables
+@cindex tunables, shared_cache_size
+@cindex non_temporal_threshold tunables
+@cindex tunables, non_temporal_threshold
 
 @deftp {Tunable namespace} glibc.tune
 Behavior of @theglibc{} can be tuned to assume specific hardware capabilities
@@ -213,3 +221,31 @@ extensions available in the processor at runtime for some architectures.  The
 @code{glibc.tune.hwcap_mask} tunable allows the user to mask out those
 capabilities at runtime, thus disabling use of those extensions.
 @end deftp
+
+@deftp Tunable glibc.tune.ifunc
+The @code{glibc.tune.ifunc=-xxx,yyy,-zzz...} tunable allows the user to
+enable CPU/ARCH feature @code{yyy}, disable CPU/ARCH feature @code{xxx}
+and @code{zzz} where the feature name is case-sensitive and has to match
+the ones in @code{sysdeps/x86/cpu-features.h}.
+
+This tunable is specific to i386 and x86-64.
+@end deftp
+
+@deftp Tunable glibc.tune.x86_data_cache_size
+The @code{glibc.tune.x86_data_cache_size} tunable allows the user to set
+data cache size in bytes for use in memory and string routines.
+
+This tunable is specific to i386 and x86-64.
+@end deftp
+
+@deftp Tunable glibc.tune.x86_shared_cache_size
+The @code{glibc.tune.x86_shared_cache_size} tunable allows the user to
+set shared cache size in bytes for use in memory and string routines.
+@end deftp
+
+@deftp Tunable glibc.tune.x86_non_temporal_threshold
+The @code{glibc.tune.x86_non_temporal_threshold} tunable allows the user
+to set threshold in bytes for non temporal store.
+
+This tunable is specific to i386 and x86-64.
+@end deftp