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Date: Fri, 10 Oct 2014 16:25:16 -0700 From: Andi Kleen <andi@...stfloor.org> To: peterz@...radead.org Cc: x86@...nel.org, linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com> Subject: [PATCH 3/4] x86: Optimize enhanced copy user fault handling From: Andi Kleen <ak@...ux.intel.com> For the enhanced copy string case we can trivially optimize the fault handling. It is just a single subtraction, as there is only one possible fault point. So get rid of handle tail for this and just do the subtraction directly. This patch is strictly not needed for the goal of making perf backtrace faster, but it will possibly help other workloads. Signed-off-by: Andi Kleen <ak@...ux.intel.com> --- arch/x86/lib/copy_user_64.S | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/x86/lib/copy_user_64.S b/arch/x86/lib/copy_user_64.S index dee945d..608caf45 100644 --- a/arch/x86/lib/copy_user_64.S +++ b/arch/x86/lib/copy_user_64.S @@ -285,8 +285,10 @@ ENTRY(copy_user_enhanced_fast_string) ret .section .fixup,"ax" -12: movl %ecx,%edx /* ecx is zerorest also */ - jmp copy_user_handle_tail + /* edx: len: ecx: actually copied bytes */ +12: sub %ecx,%edx + mov %edx,%eax + ret .previous _ASM_EXTABLE(1b,12b) -- 1.9.3 -- 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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