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));
}
/*
|