Commit 9e761bff authored Jul 03, 2023 by Uros Bizjak Committed by Alex Deucher Aug 09, 2023

drm/amdgpu: Use local64_try_cmpxchg in amdgpu_perf_read



Use local64_try_cmpxchg instead of local64_cmpxchg (*ptr, old, new) == old
in amdgpu_perf_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: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: "Pan, Xinhui" <Xinhui.Pan@amd.com>
Cc: David Airlie <airlied@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

parent 59070fd9

drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c

+2 −3

Original line number	Diff line number	Diff line
		@@ -276,9 +276,8 @@ static void amdgpu_perf_read(struct perf_event *event)
		(!pe->adev->df.funcs->pmc_get_count))
		return;

		do {
		prev = local64_read(&hwc->prev_count);

		do {
		switch (hwc->config_base) {
		case AMDGPU_PMU_EVENT_CONFIG_TYPE_DF:
		case AMDGPU_PMU_EVENT_CONFIG_TYPE_XGMI:
		@@ -289,7 +288,7 @@ static void amdgpu_perf_read(struct perf_event *event)
		count = 0;
		break;
		}
		} while (local64_cmpxchg(&hwc->prev_count, prev, count) != prev);
		} while (!local64_try_cmpxchg(&hwc->prev_count, &prev, count));

		local64_add(count - prev, &event->count);
		}