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x86, mem: memcpy_64.S: Optimize memcpy by enhanced REP MOVSB/STOSB

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Support memcpy() with enhanced rep movsb. On processors supporting enhanced
rep movsb, the alternative memcpy() function using enhanced rep movsb overrides the original function and the fast string
function.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1305671358-14478-8-git-send-email-fenghua.yu@intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Fenghua Yu 2011-05-17 15:29:16 -07:00 committed by H. Peter Anvin
parent 4307bec934
commit 101068c1f4
1 changed files with 32 additions and 13 deletions
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45
arch/x86/lib/memcpy_64.S
View file

@ -4,6 +4,7 @@
#include <asm/cpufeature.h>
#include <asm/dwarf2.h>
#include <asm/alternative-asm.h>
/*
* memcpy - Copy a memory block.
@ -37,6 +38,23 @@
.Lmemcpy_e:
.previous
/*
* memcpy_c_e() - enhanced fast string memcpy. This is faster and simpler than
* memcpy_c. Use memcpy_c_e when possible.
*
* This gets patched over the unrolled variant (below) via the
* alternative instructions framework:
*/
.section .altinstr_replacement, "ax", @progbits
.Lmemcpy_c_e:
movq %rdi, %rax
movl %edx, %ecx
rep movsb
ret
.Lmemcpy_e_e:
.previous
ENTRY(__memcpy)
ENTRY(memcpy)
CFI_STARTPROC
@ -171,21 +189,22 @@ ENDPROC(memcpy)
ENDPROC(__memcpy)
/*
* Some CPUs run faster using the string copy instructions.
* It is also a lot simpler. Use this when possible:
*/
.section .altinstructions, "a"
.align 8
.quad memcpy
.quad .Lmemcpy_c
.word X86_FEATURE_REP_GOOD
/*
* Some CPUs are adding enhanced REP MOVSB/STOSB feature
* If the feature is supported, memcpy_c_e() is the first choice.
* If enhanced rep movsb copy is not available, use fast string copy
* memcpy_c() when possible. This is faster and code is simpler than
* original memcpy().
* Otherwise, original memcpy() is used.
* In .altinstructions section, ERMS feature is placed after REG_GOOD
* feature to implement the right patch order.
*
* Replace only beginning, memcpy is used to apply alternatives,
* so it is silly to overwrite itself with nops - reboot is the
* only outcome...
*/
.byte .Lmemcpy_e - .Lmemcpy_c
.byte .Lmemcpy_e - .Lmemcpy_c
.section .altinstructions, "a"
altinstruction_entry memcpy,.Lmemcpy_c,X86_FEATURE_REP_GOOD,\
.Lmemcpy_e-.Lmemcpy_c,.Lmemcpy_e-.Lmemcpy_c
altinstruction_entry memcpy,.Lmemcpy_c_e,X86_FEATURE_ERMS, \
.Lmemcpy_e_e-.Lmemcpy_c_e,.Lmemcpy_e_e-.Lmemcpy_c_e
.previous