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| author | H.J. Lu <hjl.tools@gmail.com> | 2017-03-21 10:59:31 -0700 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2017-03-21 11:00:12 -0700 |
| commit | c15f8eb50cea7ad1a4ccece6e0982bf426d52c00 (patch) | |
| tree | da3251690c3d1f035acebce5350b0a5a0b33cc00 /sysdeps/x86_64/dl-trampoline.S | |
| parent | a640393a18329ef4044bf9213f6466cd2d1e69f3 (diff) | |
| download | glibc-c15f8eb50cea7ad1a4ccece6e0982bf426d52c00.tar.gz glibc-c15f8eb50cea7ad1a4ccece6e0982bf426d52c00.tar.xz glibc-c15f8eb50cea7ad1a4ccece6e0982bf426d52c00.zip | |
x86-64: Improve branch predication in _dl_runtime_resolve_avx512_opt [BZ #21258]
On Skylake server, _dl_runtime_resolve_avx512_opt is used to preserve
the first 8 vector registers. The code layout is
if only %xmm0 - %xmm7 registers are used
preserve %xmm0 - %xmm7 registers
if only %ymm0 - %ymm7 registers are used
preserve %ymm0 - %ymm7 registers
preserve %zmm0 - %zmm7 registers
Branch predication always executes the fallthrough code path to preserve
%zmm0 - %zmm7 registers speculatively, even though only %xmm0 - %xmm7
registers are used. This leads to lower CPU frequency on Skylake
server. This patch changes the fallthrough code path to preserve
%xmm0 - %xmm7 registers instead:
if whole %zmm0 - %zmm7 registers are used
preserve %zmm0 - %zmm7 registers
if only %ymm0 - %ymm7 registers are used
preserve %ymm0 - %ymm7 registers
preserve %xmm0 - %xmm7 registers
Tested on Skylake server.
[BZ #21258]
* sysdeps/x86_64/dl-trampoline.S (_dl_runtime_resolve_opt):
Define only if _dl_runtime_resolve is defined to
_dl_runtime_resolve_sse_vex.
* sysdeps/x86_64/dl-trampoline.h (_dl_runtime_resolve_opt):
Fallthrough to _dl_runtime_resolve_sse_vex.
Diffstat (limited to 'sysdeps/x86_64/dl-trampoline.S')
| -rw-r--r-- | sysdeps/x86_64/dl-trampoline.S | 3 |
1 files changed, 1 insertions, 2 deletions
diff --git a/sysdeps/x86_64/dl-trampoline.S b/sysdeps/x86_64/dl-trampoline.S index 33d7fcf7d0..c14c61aa58 100644 --- a/sysdeps/x86_64/dl-trampoline.S +++ b/sysdeps/x86_64/dl-trampoline.S @@ -87,11 +87,9 @@ #endif #define VEC(i) zmm##i #define _dl_runtime_resolve _dl_runtime_resolve_avx512 -#define _dl_runtime_resolve_opt _dl_runtime_resolve_avx512_opt #define _dl_runtime_profile _dl_runtime_profile_avx512 #include "dl-trampoline.h" #undef _dl_runtime_resolve -#undef _dl_runtime_resolve_opt #undef _dl_runtime_profile #undef VEC #undef VMOV @@ -145,4 +143,5 @@ # define VMOV vmovdqu #endif #define _dl_runtime_resolve _dl_runtime_resolve_sse_vex +#define _dl_runtime_resolve_opt _dl_runtime_resolve_avx512_opt #include "dl-trampoline.h" |