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| author | Peter Zijlstra <peterz@infradead.org> | 2023-04-03 11:08:58 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2023-04-05 09:58:46 +0200 |
| commit | b168098912926236bbeebaf7795eb7aab76d2b45 (patch) | |
| tree | 325d00ea96f4c6f67e86712514e4b277521475e2 /kernel/events | |
| parent | 197b6b60ae7bc51dd0814953c562833143b292aa (diff) | |
| download | lwn-b168098912926236bbeebaf7795eb7aab76d2b45.tar.gz lwn-b168098912926236bbeebaf7795eb7aab76d2b45.zip | |
perf: Optimize perf_pmu_migrate_context()
Thomas reported that offlining CPUs spends a lot of time in
synchronize_rcu() as called from perf_pmu_migrate_context() even though
he's not actually using uncore events.
Turns out, the thing is unconditionally waiting for RCU, even if there's
no actual events to migrate.
Fixes: 0cda4c023132 ("perf: Introduce perf_pmu_migrate_context()")
Reported-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lkml.kernel.org/r/20230403090858.GT4253@hirez.programming.kicks-ass.net
Diffstat (limited to 'kernel/events')
| -rw-r--r-- | kernel/events/core.c | 12 |
1 files changed, 7 insertions, 5 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index fb3e436bcd4a..115320faf1db 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -12893,12 +12893,14 @@ void perf_pmu_migrate_context(struct pmu *pmu, int src_cpu, int dst_cpu) __perf_pmu_remove(src_ctx, src_cpu, pmu, &src_ctx->pinned_groups, &events); __perf_pmu_remove(src_ctx, src_cpu, pmu, &src_ctx->flexible_groups, &events); - /* - * Wait for the events to quiesce before re-instating them. - */ - synchronize_rcu(); + if (!list_empty(&events)) { + /* + * Wait for the events to quiesce before re-instating them. + */ + synchronize_rcu(); - __perf_pmu_install(dst_ctx, dst_cpu, pmu, &events); + __perf_pmu_install(dst_ctx, dst_cpu, pmu, &events); + } mutex_unlock(&dst_ctx->mutex); mutex_unlock(&src_ctx->mutex); |