From cae701b9ccf128edea26982f73178087fc3ad180 Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Mon, 3 Jul 2023 16:52:37 +0200 Subject: [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old in perfmon_pmu_event_update. 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: Fenghua Yu Cc: Dave Jiang Cc: Vinod Koul Signed-off-by: Uros Bizjak Reviewed-by: Tom Zanussi Link: https://lore.kernel.org/r/20230703145346.5206-1-ubizjak@gmail.com Signed-off-by: Vinod Koul --- drivers/dma/idxd/perfmon.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/drivers/dma/idxd/perfmon.c b/drivers/dma/idxd/perfmon.c index d73004f..fdda6d6 100644 --- a/drivers/dma/idxd/perfmon.c +++ b/drivers/dma/idxd/perfmon.c @@ -245,12 +245,11 @@ static void perfmon_pmu_event_update(struct perf_event *event) int shift = 64 - idxd->idxd_pmu->counter_width; struct hw_perf_event *hwc = &event->hw; + prev_raw_count = local64_read(&hwc->prev_count); do { - prev_raw_count = local64_read(&hwc->prev_count); new_raw_count = perfmon_pmu_read_counter(event); - } while (local64_cmpxchg(&hwc->prev_count, prev_raw_count, - new_raw_count) != prev_raw_count); - + } while (!local64_try_cmpxchg(&hwc->prev_count, + &prev_raw_count, new_raw_count)); n = (new_raw_count << shift); p = (prev_raw_count << shift); -- 2.7.4