linux-kernel - Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED

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Message-ID: <ZBH+AaJV36y/HNXk@localhost.localdomain>
Date:   Wed, 15 Mar 2023 17:18:57 +0000
From:   Juri Lelli <juri.lelli@...hat.com>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hao Luo <haoluo@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        cgroups@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Quentin Perret <qperret@...gle.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [RFC PATCH 2/3] sched/cpuset: Keep track of SCHED_DEADLINE tasks
 in cpusets

On 15/03/23 14:49, Qais Yousef wrote:
> On 03/15/23 12:18, Juri Lelli wrote:

...

> > +void inc_dl_tasks_cs(struct task_struct *p)
> > +{
> > +	struct cpuset *cs = task_cs(p);
> 
> nit:
> 
> I *think* task_cs() assumes rcu_read_lock() is held, right?
> 
> Would it make sense to WARN_ON(!rcu_read_lock_held()) to at least
> annotate the deps?

Think we have that check in task_css_set_check()?

> Or maybe task_cs() should do that..
> 
> > +
> > +	cs->nr_deadline_tasks++;
> > +}
> > +
> > +void dec_dl_tasks_cs(struct task_struct *p)
> > +{
> > +	struct cpuset *cs = task_cs(p);
> 
> nit: ditto
> 
> > +
> > +	cs->nr_deadline_tasks--;
> > +}
> > +

...

> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 5902cbb5e751..d586a8440348 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -7683,6 +7683,16 @@ static int __sched_setscheduler(struct task_struct *p,
> >  		goto unlock;
> >  	}
> >  
> > +	/*
> > +	 * In case a task is setscheduled to SCHED_DEADLINE, or if a task is
> > +	 * moved to a different sched policy, we need to keep track of that on
> > +	 * its cpuset (for correct bandwidth tracking).
> > +	 */
> > +	if (dl_policy(policy) && !dl_task(p))
> > +		inc_dl_tasks_cs(p);
> > +	else if (dl_task(p) && !dl_policy(policy))
> > +		dec_dl_tasks_cs(p);
> > +
> 
> Would it be better to use switched_to_dl()/switched_from_dl() instead to
> inc/dec_dl_tasks_cs()?

Ah, makes sense. I'll play with this.

Thanks,
Juri