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Subject[PATCH 1/5] x86_64: use REP MOVSB in copy_page()
On my Broadwell-era Xeon copying page with REP MOVSB is ~7.8% faster
than with REP MOVSQ. Choose REP MOVSB copy_page() at runtime
with alternatives.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

arch/x86/lib/copy_page_64.S | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)

--- a/arch/x86/lib/copy_page_64.S
+++ b/arch/x86/lib/copy_page_64.S
@@ -13,13 +13,21 @@
*/
ALIGN
ENTRY(copy_page)
- ALTERNATIVE "jmp copy_page_regs", "", X86_FEATURE_REP_GOOD
+ ALTERNATIVE_2 "jmp copy_page_regs", \
+ "", X86_FEATURE_REP_GOOD, \
+ "jmp copy_page_rep_movsb", X86_FEATURE_ERMS
movl $4096/8, %ecx
rep movsq
ret
ENDPROC(copy_page)
EXPORT_SYMBOL(copy_page)

+ENTRY(copy_page_rep_movsb)
+ mov $4096, %ecx
+ rep movsb
+ ret
+ENDPROC(copy_page_rep_movsb)
+
ENTRY(copy_page_regs)
subq $2*8, %rsp
movq %rbx, (%rsp)
\
 
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