diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-06 17:16:48 +0300 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-07-10 10:52:35 +0300 |
| commit | 4c1c9dea2089374cb58505a0df6136969ff3c8b9 (patch) | |
| tree | 31ccb01e981ee0bf63342378bbd0f1e3c2ff3474 /arch/x86/events/msr.c | |
| parent | 7c2128235eff99b448af8f4b5b2933495bf1a440 (diff) | |
| download | linux-4c1c9dea2089374cb58505a0df6136969ff3c8b9.tar.xz | |
perf/x86: Use local64_try_cmpxchg
Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old.
x86 CMPXCHG instruction returns success in ZF flag, so this change saves a
compare after cmpxchg (and related move instruction in front of cmpxchg).
Also, 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.
Cc. "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230706141720.2672-1-ubizjak@gmail.com
Diffstat (limited to 'arch/x86/events/msr.c')
| -rw-r--r-- | arch/x86/events/msr.c | 8 |
1 files changed, 3 insertions, 5 deletions
diff --git a/arch/x86/events/msr.c b/arch/x86/events/msr.c index 0feaaa571303..61c59e0627d4 100644 --- a/arch/x86/events/msr.c +++ b/arch/x86/events/msr.c @@ -244,12 +244,10 @@ static void msr_event_update(struct perf_event *event) s64 delta; /* Careful, an NMI might modify the previous event value: */ -again: prev = local64_read(&event->hw.prev_count); - now = msr_read_counter(event); - - if (local64_cmpxchg(&event->hw.prev_count, prev, now) != prev) - goto again; + do { + now = msr_read_counter(event); + } while (!local64_try_cmpxchg(&event->hw.prev_count, &prev, now)); delta = now - prev; if (unlikely(event->hw.event_base == MSR_SMI_COUNT)) { |