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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
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@ -156,8 +156,8 @@ perf_event_try_update(struct perf_event *event, u64 new_raw_count, int width)
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* count to the generic event atomically:
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*/
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prev_raw_count = local64_read(&hwc->prev_count);
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if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
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new_raw_count) != prev_raw_count)
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if (!local64_try_cmpxchg(&hwc->prev_count,
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&prev_raw_count, new_raw_count))
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return 0;
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/*
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@ -129,13 +129,11 @@ u64 x86_perf_event_update(struct perf_event *event)
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* exchange a new raw count - then add that new-prev delta
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* count to the generic event atomically:
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*/
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again:
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prev_raw_count = local64_read(&hwc->prev_count);
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rdpmcl(hwc->event_base_rdpmc, new_raw_count);
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if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
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new_raw_count) != prev_raw_count)
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goto again;
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do {
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rdpmcl(hwc->event_base_rdpmc, new_raw_count);
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} while (!local64_try_cmpxchg(&hwc->prev_count,
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&prev_raw_count, new_raw_count));
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/*
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* Now we have the new raw value and have updated the prev
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@ -365,13 +365,11 @@ static void cstate_pmu_event_update(struct perf_event *event)
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struct hw_perf_event *hwc = &event->hw;
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u64 prev_raw_count, new_raw_count;
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again:
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prev_raw_count = local64_read(&hwc->prev_count);
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new_raw_count = cstate_pmu_read_counter(event);
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if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
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new_raw_count) != prev_raw_count)
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goto again;
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do {
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new_raw_count = cstate_pmu_read_counter(event);
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} while (!local64_try_cmpxchg(&hwc->prev_count,
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&prev_raw_count, new_raw_count));
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local64_add(new_raw_count - prev_raw_count, &event->count);
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}
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@ -244,12 +244,10 @@ static void msr_event_update(struct perf_event *event)
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s64 delta;
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/* Careful, an NMI might modify the previous event value: */
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again:
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prev = local64_read(&event->hw.prev_count);
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now = msr_read_counter(event);
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if (local64_cmpxchg(&event->hw.prev_count, prev, now) != prev)
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goto again;
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do {
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now = msr_read_counter(event);
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} while (!local64_try_cmpxchg(&event->hw.prev_count, &prev, now));
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delta = now - prev;
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if (unlikely(event->hw.event_base == MSR_SMI_COUNT)) {
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