[PATCH 05/15] perf, core: Optimize context switch callback invoking

[Yan, Zheng]

From: "Yan, Zheng" <zheng.z.yan@xxxxxxxxx>

So far only CPU pmu uses context switch callback and it is the
first registered pmu. So we can avoid iterating the whole pmu list.

Signed-off-by: Yan, Zheng <zheng.z.yan@xxxxxxxxx>
---
 kernel/events/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index fc97ed6..c281265 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2373,6 +2373,10 @@ static void perf_pmu_sched_task(struct task_struct *prev,
 		perf_pmu_enable(pmu);
 
 		perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
+
+		/* so far only CPU pmu uses context switch callback */
+		if (++count >= __get_cpu_var(perf_sched_cb_usages))
+			break;
 	}
 
 	rcu_read_unlock();
@@ -6492,7 +6496,7 @@ got_cpu_context:
 	if (!pmu->event_idx)
 		pmu->event_idx = perf_event_idx_default;
 
-	list_add_rcu(&pmu->entry, &pmus);
+	list_add_tail_rcu(&pmu->entry, &pmus);
 	ret = 0;
 unlock:
 	mutex_unlock(&pmus_lock);
-- 
1.8.1.4

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