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 <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Ian Rogers <[email protected]>
Cc: Adrian Hunter <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
---
arch/x86/events/amd/core.c | 3 ++-
arch/x86/events/amd/uncore.c | 6 ++++--
2 files changed, 6 insertions(+), 3 deletions(-)
diff --git a/arch/x86/events/amd/core.c b/arch/x86/events/amd/core.c
index 1fc4ce44e743..c1b8aeff7bc0 100644
--- a/arch/x86/events/amd/core.c
+++ b/arch/x86/events/amd/core.c
@@ -433,7 +433,8 @@ 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 4ccb8fa483e6..cac7c20d1aee 100644
--- a/arch/x86/events/amd/uncore.c
+++ b/arch/x86/events/amd/uncore.c
@@ -162,7 +162,8 @@ 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 +197,8 @@ 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;
}
--
2.44.0