[PATCH] [RFC] sched: Add trace_sched_waking() tracepoint to sched_ttwu_pending()

* [PATCH] [RFC] sched: Add trace_sched_waking() tracepoint to sched_ttwu_pending()
@ 2024-02-22 20:49 John Stultz
  2024-02-22 21:24 ` Phil Auld
  2024-02-22 22:57 ` Steven Rostedt
  0 siblings, 2 replies; 4+ messages in thread
From: John Stultz @ 2024-02-22 20:49 UTC (permalink / raw)
  To: LKML
  Cc: John Stultz, Ingo Molnar, Peter Zijlstra, Juri Lelli,
	Vincent Guittot, Dietmar Eggemann, Steven Rostedt, Ben Segall,
	Mel Gorman, Daniel Bristot de Oliveira, Valentin Schneider,
	kernel-team, Zimuzo Ezeozue

Zimuzo reported seeing occasional cases in perfetto traces where
tasks went from sleeping directly to trace_sched_wakeup()
without always seeing a trace_sched_waking().

Looking at the code, trace_sched_wakeup() is only called in
ttwu_do_wakeup()

The call paths that get you to ttwu_do_wakeup() are:
try_to_wake_up() -> ttwu_do_wakeup()
try_to_wake_up() -> ttwu_runnable() -> ttwu_do_wakeup()
try_to_wake_up() -> ttwu_queue() -> ttwu_do_activate() -> ttwu_do_wakeup()
sched_ttwu_pending() -> ttwu_do_activate() -> ttwu_do_wakeup()

where trace_sched_waking() is currently called only in
try_to_wake_up().

So this patch adds a trace_sched_waking() call to
sched_ttwu_pending(), so we see the same state machine
transitions.

With this change, the number of unexpected state transitions
in perfetto was greatly reduced.

This has been in my drafts for awhile, so I wanted to send
this out for thoughts/feedback.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ben Segall <bsegall@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Valentin Schneider <vschneid@redhat.com>
Cc: kernel-team@android.com
Reported-by: Zimuzo Ezeozue <zezeozue@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
---
 kernel/sched/core.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9116bcc90346..233f06360d6a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3894,6 +3894,7 @@ void sched_ttwu_pending(void *arg)
 		if (WARN_ON_ONCE(task_cpu(p) != cpu_of(rq)))
 			set_task_cpu(p, cpu_of(rq));
 
+		trace_sched_waking(p);
 		ttwu_do_activate(rq, p, p->sched_remote_wakeup ? WF_MIGRATED : 0, &rf);
 	}
 
-- 
2.44.0.rc0.258.g7320e95886-goog


^ permalink raw reply related	[flat|nested] 4+ messages in thread