Commit cae701b9 authored by Uros Bizjak's avatar Uros Bizjak Committed by Vinod Koul
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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: default avatarUros Bizjak <ubizjak@gmail.com>
Reviewed-by: default avatarTom Zanussi <tom.zanussi@linux.intel.com>
Link: https://lore.kernel.org/r/20230703145346.5206-1-ubizjak@gmail.com


Signed-off-by: default avatarVinod Koul <vkoul@kernel.org>
parent f1de55ff

drivers/dma/idxd/perfmon.c

+3 −4
Original line number Diff line number Diff line
@@ -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;



	do {

	prev_raw_count = local64_read(&hwc->prev_count);

	do {

		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);