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Message-Id: <4F218584020000780006F422@nat28.tlf.novell.com> Date: Thu, 26 Jan 2012 15:55:32 +0000 From: "Jan Beulich" <JBeulich@...e.com> To: <mingo@...e.hu>, <tglx@...utronix.de>, <hpa@...or.com> Cc: <linux-kernel@...r.kernel.org> Subject: [PATCH] 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@...e.com> --- arch/x86/lib/memcpy_64.S | 19 ++++++++++--------- 1 file changed, 10 insertions(+), 9 deletions(-) --- 3.3-rc1/arch/x86/lib/memcpy_64.S +++ 3.3-rc1-x86_64-memcpy-tail/arch/x86/lib/memcpy_64.S @@ -169,18 +169,19 @@ 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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