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perf/x86/amd: Use try_cmpxchg() in events/amd/{un,}core.c

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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@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240425101708.5025-1-ubizjak@gmail.com
This commit is contained in:
Uros Bizjak 2024-04-25 12:16:14 +02:00 committed by Ingo Molnar
parent 9d351132ed
commit cd84351c8c
2 changed files with 9 additions and 3 deletions
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4
arch/x86/events/amd/core.c
View File

@ -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;
}
}

8
arch/x86/events/amd/uncore.c
View File

@ -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;
}