From: "leilei.lin" <leilei....@alibaba-inc.com>
A performance issue caused by less strickly check in task
sched when these tasks were once attached by per-task perf_event.
A task will alloc task->perf_event_ctxp[ctxn] when it was called
by perf_event_open, and task->perf_event_ctxp[ctxn] would not
ever be freed to NULL.
if (task->perf_event_ctxp[ctxn]) // here is always true
perf_event_context_sched_in() // operate pmu
50% at most performance overhead was observed under some extreme
test case. Therefor, add a more strick check as to ctx->nr_events,
when ctx->nr_events == 0, it's no need to continue.
Signed-off-by: leilei.lin <leilei....@alibaba-inc.com>
kernel/events/core.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 426c2ff..3d86695 100644
@@ -3180,6 +3180,13 @@ static void perf_event_context_sched_in(struct
+ * We must check ctx->nr_events while holding ctx->lock, such
+ * that we serialize against perf_install_in_context().
+ if (!cpuctx->task_ctx && !ctx->nr_events)
+ goto unlock;
* We want to keep the following priority order:
@@ -3193,6 +3200,8 @@ static void perf_event_context_sched_in(struct
perf_event_sched_in(cpuctx, ctx, task);