Messages in this thread Patch in this message | | | From | Uros Bizjak <> | Subject | [PATCH] dmaengine:idxd: Use local64_try_cmpxchg in perfmon_pmu_event_update | Date | Mon, 3 Jul 2023 16:52:37 +0200 |
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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 <fenghua.yu@intel.com> Cc: Dave Jiang <dave.jiang@intel.com> Cc: Vinod Koul <vkoul@kernel.org> Signed-off-by: Uros Bizjak <ubizjak@gmail.com> --- 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 d73004f47cf4..fdda6d604262 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); -- 2.41.0
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