diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-06 16:16:48 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-07-10 09:52:35 +0200 |
| commit | 4c1c9dea2089374cb58505a0df6136969ff3c8b9 (patch) | |
| tree | 31ccb01e981ee0bf63342378bbd0f1e3c2ff3474 /arch/x86/events/intel | |
| parent | 7c2128235eff99b448af8f4b5b2933495bf1a440 (diff) | |
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/intel')
| -rw-r--r-- | arch/x86/events/intel/cstate.c | 10 |
1 files changed, 4 insertions, 6 deletions
diff --git a/arch/x86/events/intel/cstate.c b/arch/x86/events/intel/cstate.c index 835862c548cc..97035db68df2 100644 --- a/arch/x86/events/intel/cstate.c +++ b/arch/x86/events/intel/cstate.c @@ -365,13 +365,11 @@ static void cstate_pmu_event_update(struct perf_event *event) struct hw_perf_event *hwc = &event->hw; u64 prev_raw_count, new_raw_count; -again: prev_raw_count = local64_read(&hwc->prev_count); - new_raw_count = cstate_pmu_read_counter(event); - - if (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) != prev_raw_count) - goto again; + do { + new_raw_count = cstate_pmu_read_counter(event); + } while (!local64_try_cmpxchg(&hwc->prev_count, + &prev_raw_count, new_raw_count)); local64_add(new_raw_count - prev_raw_count, &event->count); } |