From 7106a5ab89c50c6b5aadea0850b40323804a922d Mon Sep 17 00:00:00 2001 From: Benjamin LaHaise Date: Sat, 10 Jan 2009 23:00:22 -0500 Subject: x86-64: remove locked instruction from switch_to() Impact: micro-optimization The patch below removes an unnecessary locked instruction from switch_to(). TIF_FORK is only ever set in copy_thread() on initial process creation, and gets cleared during the first scheduling of the process. As such, it is safe to use an unlocked test for the flag within switch_to(). Signed-off-by: Benjamin LaHaise Signed-off-by: Ingo Molnar --- arch/x86/include/asm/system.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'arch/x86/include/asm/system.h') diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h index 8e626ea33a1..fa47b1e6a86 100644 --- a/arch/x86/include/asm/system.h +++ b/arch/x86/include/asm/system.h @@ -96,15 +96,15 @@ do { \ "thread_return:\n\t" \ "movq %%gs:%P[pda_pcurrent],%%rsi\n\t" \ "movq %P[thread_info](%%rsi),%%r8\n\t" \ - LOCK_PREFIX "btr %[tif_fork],%P[ti_flags](%%r8)\n\t" \ "movq %%rax,%%rdi\n\t" \ - "jc ret_from_fork\n\t" \ + "testl %[_tif_fork],%P[ti_flags](%%r8)\n\t" \ + "jnz ret_from_fork\n\t" \ RESTORE_CONTEXT \ : "=a" (last) \ : [next] "S" (next), [prev] "D" (prev), \ [threadrsp] "i" (offsetof(struct task_struct, thread.sp)), \ [ti_flags] "i" (offsetof(struct thread_info, flags)), \ - [tif_fork] "i" (TIF_FORK), \ + [_tif_fork] "i" (_TIF_FORK), \ [thread_info] "i" (offsetof(struct task_struct, stack)), \ [pda_pcurrent] "i" (offsetof(struct x8664_pda, pcurrent)) \ : "memory", "cc" __EXTRA_CLOBBER) -- cgit v1.2.3