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From: H.J. Lu <hjl@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc/release/2.28/master] x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP Date: Thu, 27 Jan 2022 22:40:32 +0000 (GMT) [thread overview] Message-ID: <20220127224032.1606138515F3@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=b2e59f87ae10e5874bb150bd87f3b92b47b1090e commit b2e59f87ae10e5874bb150bd87f3b92b47b1090e Author: H.J. Lu <hjl.tools@gmail.com> Date: Fri Feb 26 05:36:59 2021 -0800 x86: Set Prefer_No_VZEROUPPER and add Prefer_AVX2_STRCMP 1. Set Prefer_No_VZEROUPPER if RTM is usable to avoid RTM abort triggered by VZEROUPPER inside a transactionally executing RTM region. 2. Since to compare 2 32-byte strings, 256-bit EVEX strcmp requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB, AVX2 strcmp is faster than EVEX strcmp. Add Prefer_AVX2_STRCMP to prefer AVX2 strcmp family functions. (cherry picked from commit 1da50d4bda07f04135dca39f40e79fc9eabed1f8) Diff: --- sysdeps/x86/cpu-features.c | 20 ++++++++++++++++++-- sysdeps/x86/cpu-features.h | 2 ++ sysdeps/x86/cpu-tunables.c | 3 +++ 3 files changed, 23 insertions(+), 2 deletions(-) diff --git a/sysdeps/x86/cpu-features.c b/sysdeps/x86/cpu-features.c index 4695ac80d4..5ddc8eebf4 100644 --- a/sysdeps/x86/cpu-features.c +++ b/sysdeps/x86/cpu-features.c @@ -347,8 +347,24 @@ init_cpu_features (struct cpu_features *cpu_features) cpu_features->feature[index_arch_Prefer_No_VZEROUPPER] |= bit_arch_Prefer_No_VZEROUPPER; else - cpu_features->feature[index_arch_Prefer_No_AVX512] - |= bit_arch_Prefer_No_AVX512; + { + cpu_features->feature[index_arch_Prefer_No_AVX512] + |= bit_arch_Prefer_No_AVX512; + + /* Avoid RTM abort triggered by VZEROUPPER inside a + transactionally executing RTM region. */ + if (CPU_FEATURES_CPU_P (cpu_features, RTM)) + cpu_features->feature[index_arch_Prefer_No_VZEROUPPER] + |= bit_arch_Prefer_No_VZEROUPPER; + + /* Since to compare 2 32-byte strings, 256-bit EVEX strcmp + requires 2 loads, 3 VPCMPs and 2 KORDs while AVX2 strcmp + requires 1 load, 2 VPCMPEQs, 1 VPMINU and 1 VPMOVMSKB, + AVX2 strcmp is faster than EVEX strcmp. */ + if (CPU_FEATURES_ARCH_P (cpu_features, AVX2_Usable)) + cpu_features->feature[index_arch_Prefer_AVX2_STRCMP] + |= bit_arch_Prefer_AVX2_STRCMP; + } } /* This spells out "AuthenticAMD". */ else if (ebx == 0x68747541 && ecx == 0x444d4163 && edx == 0x69746e65) diff --git a/sysdeps/x86/cpu-features.h b/sysdeps/x86/cpu-features.h index 347a4b118d..1f60296e7b 100644 --- a/sysdeps/x86/cpu-features.h +++ b/sysdeps/x86/cpu-features.h @@ -41,6 +41,7 @@ #define bit_arch_MathVec_Prefer_No_AVX512 (1 << 21) #define bit_arch_XSAVEC_Usable (1 << 22) #define bit_arch_Prefer_FSRM (1 << 23) +#define bit_arch_Prefer_AVX2_STRCMP (1 << 24) /* CPUID Feature flags. */ @@ -266,6 +267,7 @@ extern const struct cpu_features *__get_cpu_features (void) # define index_arch_MathVec_Prefer_No_AVX512 FEATURE_INDEX_1 # define index_arch_XSAVEC_Usable FEATURE_INDEX_1 # define index_arch_Prefer_FSRM FEATURE_INDEX_1 +# define index_arch_Prefer_AVX2_STRCMP FEATURE_INDEX_1 #endif /* !__ASSEMBLER__ */ diff --git a/sysdeps/x86/cpu-tunables.c b/sysdeps/x86/cpu-tunables.c index 69155a8f44..824ee76b1a 100644 --- a/sysdeps/x86/cpu-tunables.c +++ b/sysdeps/x86/cpu-tunables.c @@ -282,6 +282,9 @@ TUNABLE_CALLBACK (set_hwcaps) (tunable_val_t *valp) CHECK_GLIBC_IFUNC_ARCH_BOTH (n, cpu_features, Fast_Copy_Backward, disable, 18); + CHECK_GLIBC_IFUNC_ARCH_NEED_ARCH_BOTH + (n, cpu_features, Prefer_AVX2_STRCMP, AVX2_Usable, + disable, 18); } break; case 19:
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