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| author | H.J. Lu <hjl.tools@gmail.com> | 2020-01-25 14:19:40 -0800 |
|---|---|---|
| committer | H.J. Lu <hjl.tools@gmail.com> | 2021-01-12 04:31:55 -0800 |
| commit | 1a24bbd43e483650c7ac622f600f755229c90d23 (patch) | |
| tree | 741172df5f6b7de7dc82545d5f1bcb49746ebc23 | |
| parent | 0d9793e82a19bcef10ef7d73a26cd44b7ad30753 (diff) | |
| download | glibc-1a24bbd43e483650c7ac622f600f755229c90d23.zip glibc-1a24bbd43e483650c7ac622f600f755229c90d23.tar.gz glibc-1a24bbd43e483650c7ac622f600f755229c90d23.tar.bz2 | |
x86-64: Avoid rep movsb with short distance [BZ #27130]
When copying with "rep movsb", if the distance between source and
destination is N*4GB + [1..63] with N >= 0, performance may be very
slow. This patch updates memmove-vec-unaligned-erms.S for AVX and
AVX512 versions with the distance in RCX:
cmpl $63, %ecx
// Don't use "rep movsb" if ECX <= 63
jbe L(Don't use rep movsb")
Use "rep movsb"
Benchtests data with bench-memcpy, bench-memcpy-large, bench-memcpy-random
and bench-memcpy-walk on Skylake, Ice Lake and Tiger Lake show that its
performance impact is within noise range as "rep movsb" is only used for
data size >= 4KB.
(cherry picked from commit 3ec5d83d2a237d39e7fd6ef7a0bc8ac4c171a4a5)
| -rw-r--r-- | sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S | 21 |
1 files changed, 21 insertions, 0 deletions
diff --git a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S index bd5dc1a..092f364 100644 --- a/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S +++ b/sysdeps/x86_64/multiarch/memmove-vec-unaligned-erms.S @@ -56,6 +56,13 @@ # endif #endif +/* Avoid short distance rep movsb only with non-SSE vector. */ +#ifndef AVOID_SHORT_DISTANCE_REP_MOVSB +# define AVOID_SHORT_DISTANCE_REP_MOVSB (VEC_SIZE > 16) +#else +# define AVOID_SHORT_DISTANCE_REP_MOVSB 0 +#endif + #ifndef PREFETCH # define PREFETCH(addr) prefetcht0 addr #endif @@ -243,7 +250,21 @@ L(movsb): cmpq %r9, %rdi /* Avoid slow backward REP MOVSB. */ jb L(more_8x_vec_backward) +# if AVOID_SHORT_DISTANCE_REP_MOVSB + movq %rdi, %rcx + subq %rsi, %rcx + jmp 2f +# endif 1: +# if AVOID_SHORT_DISTANCE_REP_MOVSB + movq %rsi, %rcx + subq %rdi, %rcx +2: +/* Avoid "rep movsb" if RCX, the distance between source and destination, + is N*4GB + [1..63] with N >= 0. */ + cmpl $63, %ecx + jbe L(more_2x_vec) /* Avoid "rep movsb" if ECX <= 63. */ +# endif mov %RDX_LP, %RCX_LP rep movsb L(nop): |