[PATCH v2 6/6] perf/core: Don't need event_filter_match when merge_sched_in()

[Chengming Zhou]

There are two obselete comments in perf_cgroup_switch(), since
we don't use event_filter_match() when event_sched_out(). And
found we needn't to use event_filter_match() when sched_in too.

Because now we use the perf_event groups RB-tree to get the
exact matched perf_events, don't need to go through the
event_filter_match() to check if matched.

We can remove it in merge_sched_in() actually, but this patch
changes it to a WARN_ON_ONCE for debug purpose, and found
no warning in our stress test.

Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
---
 kernel/events/core.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4c8657b08301..744078fe2819 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -860,15 +860,11 @@ static void perf_cgroup_switch(struct task_struct *task)
 		perf_pmu_disable(cpuctx->ctx.pmu);
 
 		cpu_ctx_sched_out(cpuctx, EVENT_ALL);
-		/*
-		 * must not be done before ctxswout due
-		 * to event_filter_match() in event_sched_out()
-		 */
 		cpuctx->cgrp = cgrp;
 		/*
 		 * set cgrp before ctxsw in to allow
-		 * event_filter_match() to not have to pass
-		 * task around
+		 * visit_groups_merge() to find matched
+		 * cgroup events
 		 */
 		cpu_ctx_sched_in(cpuctx, EVENT_ALL);
 
@@ -3729,7 +3725,7 @@ static int merge_sched_in(struct perf_event *event, void *data)
 	if (event->state <= PERF_EVENT_STATE_OFF)
 		return 0;
 
-	if (!event_filter_match(event))
+	if (WARN_ON_ONCE(!event_filter_match(event)))
 		return 0;
 
 	if (group_can_go_on(event, cpuctx, *can_add_hw)) {
-- 
2.20.1