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x86: Add seperate non-temporal tunable for memset

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The tuning for non-temporal stores for memset vs memcpy is not always
the same. This includes both the exact value and whether non-temporal
stores are profitable at all for a given arch.

This patch add `x86_memset_non_temporal_threshold`. Currently we
disable non-temporal stores for non Intel vendors as the only
benchmarks showing its benefit have been on Intel hardware.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Noah Goldstein 2024-05-24 12:38:51 -05:00
parent 5bf0ab8057
commit 46b5e98ef6
7 changed files with 49 additions and 6 deletions
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16
manual/tunables.texi
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@ -52,6 +52,7 @@ glibc.elision.skip_lock_busy: 3 (min: 0, max: 2147483647)
glibc.malloc.top_pad: 0x20000 (min: 0x0, max: 0xffffffffffffffff)
glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x4040, max: 0xfffffffffffffff)
glibc.cpu.x86_memset_non_temporal_threshold: 0xc0000 (min: 0x4040, max: 0xfffffffffffffff)
glibc.cpu.x86_shstk:
glibc.pthread.stack_cache_size: 0x2800000 (min: 0x0, max: 0xffffffffffffffff)
glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
@ -495,7 +496,8 @@ thread stack originally backup by Huge Pages to default pages.
@cindex shared_cache_size tunables
@cindex tunables, shared_cache_size
@cindex non_temporal_threshold tunables
@cindex tunables, non_temporal_threshold
@cindex memset_non_temporal_threshold tunables
@cindex tunables, non_temporal_threshold, memset_non_temporal_threshold
@deftp {Tunable namespace} glibc.cpu
Behavior of @theglibc{} can be tuned to assume specific hardware capabilities
@ -574,6 +576,18 @@ like memmove and memcpy.
This tunable is specific to i386 and x86-64.
@end deftp
@deftp Tunable glibc.cpu.x86_memset_non_temporal_threshold
The @code{glibc.cpu.x86_memset_non_temporal_threshold} tunable allows
the user to set threshold in bytes for non temporal store in
memset. Non temporal stores give a hint to the hardware to move data
directly to memory without displacing other data from the cache. This
tunable is used by some platforms to determine when to use non
temporal stores memset.
This tunable is specific to i386 and x86-64.
@end deftp
@deftp Tunable glibc.cpu.x86_rep_movsb_threshold
The @code{glibc.cpu.x86_rep_movsb_threshold} tunable allows the user to
set threshold in bytes to start using "rep movsb". The value must be

8
sysdeps/x86/cacheinfo.h
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@ -35,9 +35,12 @@ long int __x86_data_cache_size attribute_hidden = 32 * 1024;
long int __x86_shared_cache_size_half attribute_hidden = 1024 * 1024 / 2;
long int __x86_shared_cache_size attribute_hidden = 1024 * 1024;
/* Threshold to use non temporal store. */
/* Threshold to use non temporal store in memmove. */
long int __x86_shared_non_temporal_threshold attribute_hidden;
/* Threshold to use non temporal store in memset. */
long int __x86_memset_non_temporal_threshold attribute_hidden;
/* Threshold to use Enhanced REP MOVSB. */
long int __x86_rep_movsb_threshold attribute_hidden = 2048;
@ -77,6 +80,9 @@ init_cacheinfo (void)
__x86_shared_non_temporal_threshold
= cpu_features->non_temporal_threshold;
__x86_memset_non_temporal_threshold
= cpu_features->memset_non_temporal_threshold;
__x86_rep_movsb_threshold = cpu_features->rep_movsb_threshold;
__x86_rep_stosb_threshold = cpu_features->rep_stosb_threshold;
__x86_rep_movsb_stop_threshold = cpu_features->rep_movsb_stop_threshold;

16
sysdeps/x86/dl-cacheinfo.h
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@ -986,6 +986,13 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
if (CPU_FEATURE_USABLE_P (cpu_features, FSRM))
rep_movsb_threshold = 2112;
/* Non-temporal stores in memset have only been tested on Intel hardware.
Until we benchmark data on other x86 processor, disable non-temporal
stores in memset. */
unsigned long int memset_non_temporal_threshold = SIZE_MAX;
if (cpu_features->basic.kind == arch_kind_intel)
memset_non_temporal_threshold = non_temporal_threshold;
/* For AMD CPUs that support ERMS (Zen3+), REP MOVSB is in a lot of
cases slower than the vectorized path (and for some alignments,
it is really slow, check BZ #30994). */
@ -1012,6 +1019,11 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
&& tunable_size <= maximum_non_temporal_threshold)
non_temporal_threshold = tunable_size;
tunable_size = TUNABLE_GET (x86_memset_non_temporal_threshold, long int, NULL);
if (tunable_size > minimum_non_temporal_threshold
&& tunable_size <= maximum_non_temporal_threshold)
memset_non_temporal_threshold = tunable_size;
tunable_size = TUNABLE_GET (x86_rep_movsb_threshold, long int, NULL);
if (tunable_size > minimum_rep_movsb_threshold)
rep_movsb_threshold = tunable_size;
@ -1032,6 +1044,9 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
TUNABLE_SET_WITH_BOUNDS (x86_non_temporal_threshold, non_temporal_threshold,
minimum_non_temporal_threshold,
maximum_non_temporal_threshold);
TUNABLE_SET_WITH_BOUNDS (
x86_memset_non_temporal_threshold, memset_non_temporal_threshold,
minimum_non_temporal_threshold, maximum_non_temporal_threshold);
TUNABLE_SET_WITH_BOUNDS (x86_rep_movsb_threshold, rep_movsb_threshold,
minimum_rep_movsb_threshold, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_rep_stosb_threshold, rep_stosb_threshold, 1,
@ -1045,6 +1060,7 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
cpu_features->data_cache_size = data;
cpu_features->shared_cache_size = shared;
cpu_features->non_temporal_threshold = non_temporal_threshold;
cpu_features->memset_non_temporal_threshold = memset_non_temporal_threshold;
cpu_features->rep_movsb_threshold = rep_movsb_threshold;
cpu_features->rep_stosb_threshold = rep_stosb_threshold;
cpu_features->rep_movsb_stop_threshold = rep_movsb_stop_threshold;

2
sysdeps/x86/dl-diagnostics-cpu.c
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@ -94,6 +94,8 @@ _dl_diagnostics_cpu (void)
cpu_features->shared_cache_size);
print_cpu_features_value ("non_temporal_threshold",
cpu_features->non_temporal_threshold);
print_cpu_features_value ("memset_non_temporal_threshold",
cpu_features->memset_non_temporal_threshold);
print_cpu_features_value ("rep_movsb_threshold",
cpu_features->rep_movsb_threshold);
print_cpu_features_value ("rep_movsb_stop_threshold",

3
sysdeps/x86/dl-tunables.list
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@ -30,6 +30,9 @@ glibc {
x86_non_temporal_threshold {
type: SIZE_T
}
x86_memset_non_temporal_threshold {
type: SIZE_T
}
x86_rep_movsb_threshold {
type: SIZE_T
# Since there is overhead to set up REP MOVSB operation, REP

4
sysdeps/x86/include/cpu-features.h
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@ -944,8 +944,10 @@ struct cpu_features
/* Shared cache size for use in memory and string routines, typically
L2 or L3 size. */
unsigned long int shared_cache_size;
/* Threshold to use non temporal store. */
/* Threshold to use non temporal store in memmove. */
unsigned long int non_temporal_threshold;
/* Threshold to use non temporal store in memset. */
unsigned long int memset_non_temporal_threshold;
/* Threshold to use "rep movsb". */
unsigned long int rep_movsb_threshold;
/* Threshold to stop using "rep movsb". */

6
sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
View File

@ -24,9 +24,9 @@
5. If size is more to 4 * VEC_SIZE, align to 1 * VEC_SIZE with
4 VEC stores and store 4 * VEC at a time until done.
6. On machines ERMS feature, if size is range
[__x86_rep_stosb_threshold, __x86_shared_non_temporal_threshold)
[__x86_rep_stosb_threshold, __x86_memset_non_temporal_threshold)
then REP STOSB will be used.
7. If size >= __x86_shared_non_temporal_threshold, use a
7. If size >= __x86_memset_non_temporal_threshold, use a
non-temporal stores. */
#include <sysdep.h>
@ -318,7 +318,7 @@ L(return_vzeroupper):
/* If no USE_LESS_VEC_MASK put L(stosb_local) here. Will be in
range for 2-byte jump encoding. */
L(stosb_local):
cmp __x86_shared_non_temporal_threshold(%rip), %RDX_LP
cmp __x86_memset_non_temporal_threshold(%rip), %RDX_LP
jae L(nt_memset)
movzbl %sil, %eax
mov %RDX_LP, %RCX_LP