diff options
| author | Benjamin LaHaise <bcrl@kvack.org> | 2009-01-10 23:00:22 -0500 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2009-01-11 05:05:33 +0100 |
| commit | 7106a5ab89c50c6b5aadea0850b40323804a922d (patch) | |
| tree | d4ce5df5ff89da035b6dd092bbe089757def7c34 /arch/x86 | |
| parent | c59765042f53a79a7a65585042ff463b69cb248c (diff) | |
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 <bcrl@kvack.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'arch/x86')
| -rw-r--r-- | arch/x86/include/asm/system.h | 6 | ||||
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 2 |
2 files changed, 5 insertions, 3 deletions
diff --git a/arch/x86/include/asm/system.h b/arch/x86/include/asm/system.h index 8e626ea33a1a..fa47b1e6a866 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) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index e28c7a987793..38dd37458e44 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -408,6 +408,8 @@ END(save_paranoid) ENTRY(ret_from_fork) DEFAULT_FRAME + LOCK ; btr $TIF_FORK,TI_flags(%r8) + push kernel_eflags(%rip) CFI_ADJUST_CFA_OFFSET 8 popf # reset kernel eflags |