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 <[email protected]> Cc: Joonas Lahtinen <[email protected]> Cc: Rodrigo Vivi <[email protected]> Cc: Tvrtko Ursulin <[email protected]> Cc: David Airlie <[email protected]> Cc: Daniel Vetter <[email protected]> Signed-off-by: Uros Bizjak <[email protected]> --- drivers/gpu/drm/i915/i915_pmu.c | 9 ++++----- 1 file 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); } -- 2.41.0
