Commit-ID: 9d8e22777e66f420e46490e9fc6f8cb7e0e2222b Gitweb: http://git.kernel.org/tip/9d8e22777e66f420e46490e9fc6f8cb7e0e2222b Author: Jan Beulich <JBeulich@xxxxxxxx> AuthorDate: Thu, 26 Jan 2012 15:55:32 +0000 Committer: Ingo Molnar <mingo@xxxxxxx> CommitDate: Thu, 26 Jan 2012 21:19:20 +0100 x86-64: Handle byte-wise tail copying in memcpy() without a loop While hard to measure, reducing the number of possibly/likely mis-predicted branches can generally be expected to be slightly better. Other than apparent at the first glance, this also doesn't grow the function size (the alignment gap to the next function just gets smaller). Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/4F218584020000780006F422@xxxxxxxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxx> --- arch/x86/lib/memcpy_64.S | 19 ++++++++++--------- 1 files changed, 10 insertions(+), 9 deletions(-) diff --git a/arch/x86/lib/memcpy_64.S b/arch/x86/lib/memcpy_64.S index 1235b04..1c273be 100644 --- a/arch/x86/lib/memcpy_64.S +++ b/arch/x86/lib/memcpy_64.S @@ -164,18 +164,19 @@ ENTRY(memcpy) retq .p2align 4 .Lless_3bytes: - cmpl $0, %edx - je .Lend + subl $1, %edx + jb .Lend /* * Move data from 1 bytes to 3 bytes. */ -.Lloop_1: - movb (%rsi), %r8b - movb %r8b, (%rdi) - incq %rdi - incq %rsi - decl %edx - jnz .Lloop_1 + movzbl (%rsi), %ecx + jz .Lstore_1byte + movzbq 1(%rsi), %r8 + movzbq (%rsi, %rdx), %r9 + movb %r8b, 1(%rdi) + movb %r9b, (%rdi, %rdx) +.Lstore_1byte: + movb %cl, (%rdi) .Lend: retq -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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