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.
__perf_event_task_sched_in()
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
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3180,6 +3180,13 @@ static void perf_event_context_sched_in(struct
perf_event_context *ctx,
return;
perf_ctx_lock(cpuctx, ctx);
+ /*
+ * 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;
+
perf_pmu_disable(ctx->pmu);
/*
* We want to keep the following priority order:
@@ -3193,6 +3200,8 @@ static void perf_event_context_sched_in(struct
perf_event_context *ctx,
cpu_ctx_sched_out(cpuctx, EVENT_FLEXIBLE);
perf_event_sched_in(cpuctx, ctx, task);
perf_pmu_enable(ctx->pmu);
+
+unlock:
perf_ctx_unlock(cpuctx, ctx);
}
--
2.8.4.31.g9ed660f
