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| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-03 17:08:18 +0200 |
|---|---|---|
| committer | Jani Nikula <jani.nikula@intel.com> | 2023-10-05 13:20:40 +0300 |
| commit | 6097cdac5af6115041dd7835670650c9c3633877 (patch) | |
| tree | 75d193f9f09ff15334532b5cc569bb0ebaa38a65 /drivers | |
| parent | 5846cdfd3d58852cdc991e589de7535151a47a4e (diff) | |
| download | lwn-6097cdac5af6115041dd7835670650c9c3633877.tar.gz lwn-6097cdac5af6115041dd7835670650c9c3633877.zip | |
drm/i915/pmu: Use local64_try_cmpxchg in i915_pmu_event_read
Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
in i915_pmu_event_read. 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: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230703150859.6176-1-ubizjak@gmail.com
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/gpu/drm/i915/i915_pmu.c | 9 |
1 files changed, 4 insertions, 5 deletions
diff --git a/drivers/gpu/drm/i915/i915_pmu.c b/drivers/gpu/drm/i915/i915_pmu.c index d35973b41186..108b675088ba 100644 --- a/drivers/gpu/drm/i915/i915_pmu.c +++ b/drivers/gpu/drm/i915/i915_pmu.c @@ -696,12 +696,11 @@ static void i915_pmu_event_read(struct perf_event *event) event->hw.state = PERF_HES_STOPPED; return; } -again: - prev = local64_read(&hwc->prev_count); - new = __i915_pmu_event_read(event); - if (local64_cmpxchg(&hwc->prev_count, prev, new) != prev) - goto again; + prev = local64_read(&hwc->prev_count); + do { + new = __i915_pmu_event_read(event); + } while (!local64_try_cmpxchg(&hwc->prev_count, &prev, new)); local64_add(new - prev, &event->count); } |