AcoSail/kernel_optimize_test
8
0
Fork 0
forked from luck/tmp_suning_uos_patched
Code Pull Requests Activity

x86/lib/copy_page_64.S: Use generic ALTERNATIVE macro

Browse Source 
... instead of the semi-version with the spelled out sections.

What is more, make the REP_GOOD version be the default copy_page()
version as the majority of the relevant x86 CPUs do set
X86_FEATURE_REP_GOOD. Thus, copy_page gets compiled to:

  ffffffff8130af80 <copy_page>:
  ffffffff8130af80:       e9 0b 00 00 00          jmpq   ffffffff8130af90 <copy_page_regs>
  ffffffff8130af85:       b9 00 02 00 00          mov    $0x200,%ecx
  ffffffff8130af8a:       f3 48 a5                rep movsq %ds:(%rsi),%es:(%rdi)
  ffffffff8130af8d:       c3                      retq
  ffffffff8130af8e:       66 90                   xchg   %ax,%ax

  ffffffff8130af90 <copy_page_regs>:
  ...

and after the alternatives have run, the JMP to the old, unrolled
version gets NOPed out:

  ffffffff8130af80 <copy_page>:
  ffffffff8130af80:  66 66 90		xchg   %ax,%ax
  ffffffff8130af83:  66 90		xchg   %ax,%ax
  ffffffff8130af85:  b9 00 02 00 00	mov    $0x200,%ecx
  ffffffff8130af8a:  f3 48 a5		rep movsq %ds:(%rsi),%es:(%rdi)
  ffffffff8130af8d:  c3			retq

On modern uarches, those NOPs are cheaper than the unconditional JMP
previously.

Signed-off-by: Borislav Petkov <bp@suse.de>
This commit is contained in:
Borislav Petkov 2015-01-12 18:19:40 +01:00
parent 4fd4b6e553
commit 090a3f6155
1 changed files with 12 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
arch/x86/lib/copy_page_64.S
View File

@ -2,23 +2,26 @@
#include <linux/linkage.h>
#include <asm/dwarf2.h>
#include <asm/cpufeature.h>
#include <asm/alternative-asm.h>
/*
* Some CPUs run faster using the string copy instructions (sane microcode).
* It is also a lot simpler. Use this when possible. But, don't use streaming
* copy unless the CPU indicates X86_FEATURE_REP_GOOD. Could vary the
* prefetch distance based on SMP/UP.
*/
ALIGN
copy_page_rep:
ENTRY(copy_page)
CFI_STARTPROC
ALTERNATIVE "jmp copy_page_regs", "", X86_FEATURE_REP_GOOD
movl $4096/8, %ecx
rep movsq
ret
CFI_ENDPROC
ENDPROC(copy_page_rep)
ENDPROC(copy_page)
/*
* Don't use streaming copy unless the CPU indicates X86_FEATURE_REP_GOOD.
* Could vary the prefetch distance based on SMP/UP.
*/
ENTRY(copy_page)
ENTRY(copy_page_regs)
CFI_STARTPROC
subq $2*8, %rsp
CFI_ADJUST_CFA_OFFSET 2*8
@ -90,21 +93,5 @@ ENTRY(copy_page)
addq $2*8, %rsp
CFI_ADJUST_CFA_OFFSET -2*8
ret
.Lcopy_page_end:
CFI_ENDPROC
ENDPROC(copy_page)
/* Some CPUs run faster using the string copy instructions.
It is also a lot simpler. Use this when possible */
#include <asm/cpufeature.h>
.section .altinstr_replacement,"ax"
1: .byte 0xeb /* jmp <disp8> */
.byte (copy_page_rep - copy_page) - (2f - 1b) /* offset */
2:
.previous
.section .altinstructions,"a"
altinstruction_entry copy_page, 1b, X86_FEATURE_REP_GOOD, \
.Lcopy_page_end-copy_page, 2b-1b, 0
.previous
ENDPROC(copy_page_regs)