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| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-08 10:10:57 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-07-10 09:52:35 +0200 |
| commit | 28fd85a10a2a73658c6e26056d9e093de06b5a22 (patch) | |
| tree | 2f5baf61f8679a758238d02b337b3a3bc515ca57 /kernel/events | |
| parent | perf/x86: Use local64_try_cmpxchg (diff) | |
| download | linux-28fd85a10a2a73658c6e26056d9e093de06b5a22.tar.xz linux-28fd85a10a2a73658c6e26056d9e093de06b5a22.zip | |
perf/core: Use local64_try_cmpxchg in perf_swevent_set_period
Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
in perf_swevent_set_period. 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.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20230708081129.45915-1-ubizjak@gmail.com
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/core.c | 18 |
1 files changed, 9 insertions, 9 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 78ae7b6f90fd..f84e2640ea2f 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -9595,16 +9595,16 @@ u64 perf_swevent_set_period(struct perf_event *event) hwc->last_period = hwc->sample_period; -again: - old = val = local64_read(&hwc->period_left); - if (val < 0) - return 0; + old = local64_read(&hwc->period_left); + do { + val = old; + if (val < 0) + return 0; - nr = div64_u64(period + val, period); - offset = nr * period; - val -= offset; - if (local64_cmpxchg(&hwc->period_left, old, val) != old) - goto again; + nr = div64_u64(period + val, period); + offset = nr * period; + val -= offset; + } while (!local64_try_cmpxchg(&hwc->period_left, &old, val)); return nr; } |