6.10-stable review patch. If anyone has any objections, please let me know.
------------------
From: Uros Bizjak <ubizjak@xxxxxxxxx>
[ Upstream commit cd84351c8c1baec86342d784feb884ace007d51c ]
Replace this pattern in events/amd/{un,}core.c:
cmpxchg(*ptr, old, new) == old
... with the simpler and faster:
try_cmpxchg(*ptr, &old, new)
The x86 CMPXCHG instruction returns success in the ZF flag, so this change
saves a compare after the CMPXCHG.
No functional change intended.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240425101708.5025-1-ubizjak@xxxxxxxxx
Stable-dep-of: f73cefa3b72e ("perf/x86: Fix smp_processor_id()-in-preemptible warnings")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/events/amd/core.c | 4 +++-
arch/x86/events/amd/uncore.c | 8 ++++++--
2 files changed, 9 insertions(+), 3 deletions(-)
diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 1fc4ce44e743c..18bfe3451f3aa 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -433,7 +433,9 @@ static void __amd_put_nb_event_constraints(struct cpu_hw_events *cpuc,
* when we come here
*/
for (i = 0; i < x86_pmu.num_counters; i++) {
- if (cmpxchg(nb->owners + i, event, NULL) == event)
+ struct perf_event *tmp = event;
+
+ if (try_cmpxchg(nb->owners + i, &tmp, NULL))
break;
}
}
diff --git a/arch/x86/events/amd/uncore.c b/arch/x86/events/amd/uncore.c
index 5a4bfe9aea237..0bfde2ea5cb8c 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -162,7 +162,9 @@ static int amd_uncore_add(struct perf_event *event, int flags)
/* if not, take the first available counter */
hwc->idx = -1;
for (i = 0; i < pmu->num_counters; i++) {
- if (cmpxchg(&ctx->events[i], NULL, event) == NULL) {
+ struct perf_event *tmp = NULL;
+
+ if (try_cmpxchg(&ctx->events[i], &tmp, event)) {
hwc->idx = i;
break;
}
@@ -196,7 +198,9 @@ static void amd_uncore_del(struct perf_event *event, int flags)
event->pmu->stop(event, PERF_EF_UPDATE);
for (i = 0; i < pmu->num_counters; i++) {
- if (cmpxchg(&ctx->events[i], event, NULL) == event)
+ struct perf_event *tmp = event;
+
+ if (try_cmpxchg(&ctx->events[i], &tmp, NULL))
break;
}
--
2.43.0
