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| author | Uros Bizjak <ubizjak@gmail.com> | 2023-07-03 17:52:37 +0300 |
|---|---|---|
| committer | Vinod Koul <vkoul@kernel.org> | 2023-08-01 21:02:06 +0300 |
| commit | cae701b9ccf128edea26982f73178087fc3ad180 (patch) | |
| tree | 7056cd55ddf4cfe83b07414e6b4b17a34128e18e | |
| parent | f1de55ff7c704b48389987f6c71ca31dc8cffe8d (diff) | |
| download | linux-cae701b9ccf128edea26982f73178087fc3ad180.tar.xz | |
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 <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>
Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Link: https://lore.kernel.org/r/20230703145346.5206-1-ubizjak@gmail.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
| -rw-r--r-- | drivers/dma/idxd/perfmon.c | 7 |
1 files 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); |