linux-kernel - Re: [PATCH][V2] sched/rt: Print curr when RT throttling activated

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Date: Mon, 1 Apr 2024 18:47:58 +0300
From: Alexandru Ardelean <alex@...uggie.ro>
To: linux-kernel@...r.kernel.org
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com, 
	vincent.guittot@...aro.org, dietmar.eggemann@....com, rostedt@...dmis.org, 
	bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com, 
	tian.xianting@....com, steffen.aschbacher@...hl.de, 
	gregkh@...uxfoundation.org
Subject: Re: [PATCH][V2] sched/rt: Print curr when RT throttling activated

On Thu, Jul 13, 2023 at 11:07 PM Alexandru Ardelean <alex@...uggie.ro> wrote:
>
> On Tue, May 16, 2023 at 3:22 PM Alexandru Ardelean <alex@...uggiero> wrote:
> >
> > From: Xianting Tian <tian.xianting@....com>
> >
> > We may meet the issue, that one RT thread occupied the cpu by 950ms/1s,
> > The RT thread maybe is a business thread or other unknown thread.
> >
> > Currently, it only outputs the print "sched: RT throttling activated"
> > when RT throttling happen. It is hard to know what is the RT thread,
> > For further analysis, we need add more prints.
> >
> > This patch is to print current RT task when RT throttling activated,
> > It help us to know what is the RT thread in the first time.
> >
>
> Adding Greg on this patch, since it 's been a while.
> And also: ping :)

Ping on this :)

Thanks
Alex

>
> > Tested-by: Alexandru Ardelean <alex@...uggie.ro>
> > Signed-off-by: Xianting Tian <tian.xianting@....com>
> > ---
> >
> > Initial patch submission:
> >   https://lore.kernel.org/all/f3265adc26d4416dacf157f61fa60ad6@h3c.com/T/
> >
> > We've been having some issues of our own with some applications + some RT
> > configuration == some threads endded up taking too much CPU time.
> > This patch came in quite in handy to see in logs which thread is more
> > problematic.
> >
> > We've applied this patch onto a 5.10.116 tree. It did need a bit of
> > re-applying since some context has changed since the initial version (hence
> > the V2 tag).
> > Since 5.10.116 (where we used it), it applied nicely to the latest/current
> > linux-next tree (hence the Tested-by tag).
> >
> > It would be nice to apply this to the mainline kernel and have this handy.
> >
> >  kernel/sched/rt.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> > index 00e0e5074115..44b161e42733 100644
> > --- a/kernel/sched/rt.c
> > +++ b/kernel/sched/rt.c
> > @@ -995,7 +995,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
> >         return rt_task_of(rt_se)->prio;
> >  }
> >
> > -static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
> > +static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, struct task_struct *curr)
> >  {
> >         u64 runtime = sched_rt_runtime(rt_rq);
> >
> > @@ -1019,7 +1019,8 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
> >                  */
> >                 if (likely(rt_b->rt_runtime)) {
> >                         rt_rq->rt_throttled = 1;
> > -                       printk_deferred_once("sched: RT throttling activated\n");
> > +                       printk_deferred_once("sched: RT throttling activated (curr: pid %d, comm %s)\n",
> > +                                               curr->pid, curr->comm);
> >                 } else {
> >                         /*
> >                          * In case we did anyway, make it go away,
> > @@ -1074,7 +1075,7 @@ static void update_curr_rt(struct rq *rq)
> >                 if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
> >                         raw_spin_lock(&rt_rq->rt_runtime_lock);
> >                         rt_rq->rt_time += delta_exec;
> > -                       exceeded = sched_rt_runtime_exceeded(rt_rq);
> > +                       exceeded = sched_rt_runtime_exceeded(rt_rq, curr);
> >                         if (exceeded)
> >                                 resched_curr(rq);
> >                         raw_spin_unlock(&rt_rq->rt_runtime_lock);
> > --
> > 2.40.1
> >