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.deuc...@amd.com>
Cc: "Christian König" <christian.koe...@amd.com>
Cc: "Pan, Xinhui" <xinhui....@amd.com>
Cc: David Airlie <airl...@gmail.com>
Cc: Daniel Vetter <dan...@ffwll.ch>
Signed-off-by: Uros Bizjak <ubiz...@gmail.com>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c
index 71ee361d0972..6e91ea1de5aa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pmu.c
@@ -276,9 +276,8 @@ static void amdgpu_perf_read(struct perf_event *event)
(!pe->adev->df.funcs->pmc_get_count))
return;
+ prev = local64_read(&hwc->prev_count);
do {
- prev = local64_read(&hwc->prev_count);
-
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);
}
--
2.41.0
