The following commit has been merged into the x86/asm branch of tip: Commit-ID: b8e3dfa16ec55f310dd95831614af3d24abf5ed5 Gitweb: https://git.kernel.org/tip/b8e3dfa16ec55f310dd95831614af3d24abf5ed5 Author: Uros Bizjak <ubizjak@xxxxxxxxx> AuthorDate: Wed, 30 Aug 2023 17:13:57 +02:00 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitterDate: Fri, 15 Sep 2023 13:19:22 +02:00 x86/percpu: Use raw_cpu_try_cmpxchg() in preempt_count_set() Use raw_cpu_try_cmpxchg() instead of raw_cpu_cmpxchg(*ptr, old, new) == old. x86 CMPXCHG instruction returns success in ZF flag, so this change saves a compare after CMPXCHG (and related MOV instruction in front of CMPXCHG). Also, raw_cpu_try_cmpxchg() implicitly assigns old *ptr value to "old" when cmpxchg fails. There is no need to re-read the value in the loop. No functional change intended. Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20230830151623.3900-2-ubizjak@xxxxxxxxx --- arch/x86/include/asm/preempt.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 2d13f25..4527e14 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -31,11 +31,11 @@ static __always_inline void preempt_count_set(int pc) { int old, new; + old = raw_cpu_read_4(pcpu_hot.preempt_count); do { - old = raw_cpu_read_4(pcpu_hot.preempt_count); new = (old & PREEMPT_NEED_RESCHED) | (pc & ~PREEMPT_NEED_RESCHED); - } while (raw_cpu_cmpxchg_4(pcpu_hot.preempt_count, old, new) != old); + } while (!raw_cpu_try_cmpxchg_4(pcpu_hot.preempt_count, &old, new)); } /*