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x86: Add Avoid_STOSB tunable to allow NT memset without ERMS

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The goal of this flag is to allow targets which don't prefer/have ERMS
to still access the non-temporal memset implementation.

There are 4 cases for tuning memset:
    1) `Avoid_STOSB && Avoid_Non_Temporal_Memset`
        - Memset with temporal stores
    2) `Avoid_STOSB && !Avoid_Non_Temporal_Memset`
        - Memset with temporal/non-temporal stores. Non-temporal path
          goes through `rep stosb` path. We accomplish this by setting
          `x86_rep_stosb_threshold` to
          `x86_memset_non_temporal_threshold`.
    3) `!Avoid_STOSB && Avoid_Non_Temporal_Memset`
        - Memset with temporal stores/`rep stosb`
    3) `!Avoid_STOSB && !Avoid_Non_Temporal_Memset`
        - Memset with temporal stores/`rep stosb`/non-temporal stores.
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>
This commit is contained in:
Noah Goldstein 2024-08-14 14:37:31 +08:00 committed by H.J. Lu
parent b93dddfaf4
commit f446d90fe6
6 changed files with 53 additions and 12 deletions
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4
sysdeps/x86/cpu-features.c
View File

@ -1119,6 +1119,10 @@ https://www.intel.com/content/www/us/en/support/articles/000059422/processors.ht
if (CPU_FEATURES_CPU_P (cpu_features, CMOV))
cpu_features->preferred[index_arch_I686] |= bit_arch_I686;
/* No ERMS, we want to avoid stosb for memset. */
if (!CPU_FEATURE_USABLE_P (cpu_features, ERMS))
cpu_features->preferred[index_arch_Avoid_STOSB] |= bit_arch_Avoid_STOSB;
#if !HAS_CPUID
no_cpuid:
#endif

2
sysdeps/x86/cpu-tunables.c
View File

@ -193,6 +193,8 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp)
11);
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Prefer_FSRM,
11);
CHECK_GLIBC_IFUNC_PREFERRED_BOTH (n, cpu_features, Avoid_STOSB,
11);
CHECK_GLIBC_IFUNC_PREFERRED_NEED_BOTH (n, cpu_features,
Slow_SSE4_2,
SSE4_2,

34
sysdeps/x86/dl-cacheinfo.h
View File

@ -1041,18 +1041,42 @@ dl_init_cacheinfo (struct cpu_features *cpu_features)
slightly better than ERMS. */
rep_stosb_threshold = SIZE_MAX;
/*
For memset, the non-temporal implementation is only accessed through the
stosb code. ie:
```
if (size >= rep_stosb_thresh)
{
if (size >= non_temporal_thresh)
{
do_non_temporal ();
}
do_stosb ();
}
do_normal_vec_loop ();
```
So if we prefer non-temporal, set `rep_stosb_thresh = non_temporal_thresh`
to enable the implementation. If `rep_stosb_thresh = non_temporal_thresh`,
`rep stosb` will never be used.
*/
TUNABLE_SET_WITH_BOUNDS (x86_memset_non_temporal_threshold,
memset_non_temporal_threshold,
minimum_non_temporal_threshold, SIZE_MAX);
/* Do `rep_stosb_thresh = non_temporal_thresh` after setting/getting the
final value of `x86_memset_non_temporal_threshold`. In some cases this can
be a matter of correctness. */
if (CPU_FEATURES_ARCH_P (cpu_features, Avoid_STOSB))
rep_stosb_threshold
= TUNABLE_GET (x86_memset_non_temporal_threshold, long int, NULL);
TUNABLE_SET_WITH_BOUNDS (x86_rep_stosb_threshold, rep_stosb_threshold, 1,
SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_data_cache_size, data, 0, SIZE_MAX);
TUNABLE_SET_WITH_BOUNDS (x86_shared_cache_size, shared, 0, SIZE_MAX);
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, SIZE_MAX);
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,
SIZE_MAX);
unsigned long int rep_movsb_stop_threshold;
/* Setting the upper bound of ERMS to the computed value of

1
sysdeps/x86/include/cpu-features-preferred_feature_index_1.def
View File

@ -34,3 +34,4 @@ BIT (MathVec_Prefer_No_AVX512)
BIT (Prefer_FSRM)
BIT (Avoid_Short_Distance_REP_MOVSB)
BIT (Avoid_Non_Temporal_Memset)
BIT (Avoid_STOSB)

6
sysdeps/x86/tst-hwcap-tunables.c
View File

@ -60,7 +60,8 @@ static const struct test_t
/* Disable everything. */
"-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX512F,-AVX512VL,"
"-SSE4_1,-SSE4_2,-SSSE3,-Fast_Unaligned_Load,-ERMS,"
"-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset",
"-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset,"
"-Avoid_STOSB",
test_1,
array_length (test_1)
},
@ -68,7 +69,8 @@ static const struct test_t
/* Same as before, but with some empty suboptions. */
",-,-Prefer_ERMS,-Prefer_FSRM,-AVX,-AVX2,-AVX512F,-AVX512VL,"
"-SSE4_1,-SSE4_2,-SSSE3,-Fast_Unaligned_Load,,-,"
"-ERMS,-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset,-,",
"-ERMS,-AVX_Fast_Unaligned_Load,-Avoid_Non_Temporal_Memset,"
"-Avoid_STOSB,-,",
test_1,
array_length (test_1)
}

18
sysdeps/x86_64/multiarch/ifunc-memset.h
View File

@ -46,6 +46,13 @@ extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2_unaligned)
extern __typeof (REDIRECT_NAME) OPTIMIZE (sse2_unaligned_erms)
attribute_hidden;
static inline int
prefer_erms_nt_impl (const struct cpu_features *cpu_features)
{
return CPU_FEATURE_USABLE_P (cpu_features, ERMS)
|| !CPU_FEATURES_ARCH_P (cpu_features, Avoid_Non_Temporal_Memset);
}
static inline void *
IFUNC_SELECTOR (void)
{
@ -61,7 +68,7 @@ IFUNC_SELECTOR (void)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
{
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
if (prefer_erms_nt_impl (cpu_features))
return OPTIMIZE (avx512_unaligned_erms);
return OPTIMIZE (avx512_unaligned);
@ -76,7 +83,7 @@ IFUNC_SELECTOR (void)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, AVX512BW)
&& X86_ISA_CPU_FEATURE_USABLE_P (cpu_features, BMI2))
{
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
if (prefer_erms_nt_impl (cpu_features))
return OPTIMIZE (evex_unaligned_erms);
return OPTIMIZE (evex_unaligned);
@ -84,7 +91,7 @@ IFUNC_SELECTOR (void)
if (CPU_FEATURE_USABLE_P (cpu_features, RTM))
{
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
if (prefer_erms_nt_impl (cpu_features))
return OPTIMIZE (avx2_unaligned_erms_rtm);
return OPTIMIZE (avx2_unaligned_rtm);
@ -93,14 +100,15 @@ IFUNC_SELECTOR (void)
if (X86_ISA_CPU_FEATURES_ARCH_P (cpu_features,
Prefer_No_VZEROUPPER, !))
{
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
if (prefer_erms_nt_impl (cpu_features))
return OPTIMIZE (avx2_unaligned_erms);
return OPTIMIZE (avx2_unaligned);
}
}
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS))
if (CPU_FEATURE_USABLE_P (cpu_features, ERMS)
|| !CPU_FEATURES_ARCH_P (cpu_features, Avoid_Non_Temporal_Memset))
return OPTIMIZE (sse2_unaligned_erms);
return OPTIMIZE (sse2_unaligned);