linux-kernel - Re: [PATCH] sched: Increase sched_tick

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Message-ID: <20250916124912.GA179793@pauld.westford.csb>
Date: Tue, 16 Sep 2025 08:49:12 -0400
From: Phil Auld <pauld@...hat.com>
To: "wangtao (EQ)" <wangtao554@...wei.com>
Cc: frederic@...nel.org, bsegall@...gle.com, dietmar.eggemann@....com,
	juri.lelli@...hat.com, linux-kernel@...r.kernel.org,
	mgorman@...e.de, mingo@...hat.com, peterz@...radead.org,
	rostedt@...dmis.org, tanghui20@...wei.com, tglx@...utronix.de,
	vincent.guittot@...aro.org, zhangqiao22@...wei.com,
	Waiman Long <longman@...hat.com>
Subject: Re: [PATCH] sched: Increase sched_tick_remote timeout

On Tue, Sep 16, 2025 at 04:44:39PM +0800 wangtao (EQ) wrote:
> Increasing timeout alerts can reduce the probability of deadlocks. However, in the 'sched_tick_remote' method, there are 'WARN_ON_ONCE(rq->curr!= rq->donor)' and 'assert_clock_updated' in 'rq_clock_task'. Regardless of why these alerts are triggered, once they are triggered, 'printk' is called, which still leaves potential deadlock issues. Is there a better way to address these problems?
>

I'm not specically trying to solve the printk deadlock problem. My patch is
to make this particular warning go away by reducing the false positives.
That's tangential to your original posting. 

You can use the new printk mechanism with an atomic console to get around
the printk bug I think.

I think you could also use a serial console instead of a framebuffer based
console.


Cheers,
Phil



> 在 2025/9/12 0:13, Phil Auld 写道:
> > Increase the sched_tick_remote WARN_ON timeout to remove false
> > positives due to temporarily busy HK cpus. The suggestion
> > was 30 seconds to catch really stuck remote tick processing
> > but not trigger it too easily.
> > 
> > Signed-off-by: Phil Auld <pauld@...hat.com>
> > Suggested-by: Frederic Weisbecker <frederic@...nel.org>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Frederic Weisbecker <frederic@...nel.org>
> > ---
> >   kernel/sched/core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index be00629f0ba4..ef90d358252d 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -5724,7 +5724,7 @@ static void sched_tick_remote(struct work_struct *work)
> >   				 * reasonable amount of time.
> >   				 */
> >   				u64 delta = rq_clock_task(rq) - curr->se.exec_start;
> > -				WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 3);
> > +				WARN_ON_ONCE(delta > (u64)NSEC_PER_SEC * 30);
> >   			}
> >   			curr->sched_class->task_tick(rq, curr, 0);
> 

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