linux-kernel - Re: [PATCH v3] sched: async unthrottling for cfs bandwidth

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Date:   Thu, 24 Nov 2022 10:12:43 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Aaron Lu <aaron.lu@...el.com>, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Michal Koutný <mkoutny@...e.com>,
        Christian Brauner <brauner@...nel.org>,
        Zefan Li <lizefan.x@...edance.com>
Subject: Re: [PATCH v3] sched: async unthrottling for cfs bandwidth

On Tue, Nov 22, 2022 at 11:41:04AM -0800, Josh Don wrote:
> > > +        */
> > > +       if (local_unthrottle) {
> > > +               rq = cpu_rq(this_cpu);
> > > +               rq_lock_irqsave(rq, &rf);
> >
> > Should we add:
> >                 if (cfs_rq_throttled(local_unthrottle))
> >
> > before calling into unthrottle_cfs_rq_async(local_unthrottle) to avoid a
> > potential WARN?
> >
> > As for whether the local cfs_rq can be unthrottled now after rq lock is
> > re-acquired, I suppose it can be. e.g. another user sets a new quota to
> > this task group during the window of rq lock gets dropped in the above
> > loop and re-acquired here IIUC.
> >
> > > +               unthrottle_cfs_rq_async(local_unthrottle);
> > > +               rq_unlock_irqrestore(rq, &rf);
> > > +       }
> > > +
> > >         return throttled;
> > >  }
> 
> Yes, we should add that check due to the case you described with a
> user concurrently configuring bandwidth. And as long as we're doing
> that, we might as well make this unthrottle_cfs_rq() instead and snip
> the comment. Peter, would you mind adding that delta?

Done, should be pushed into the queue.git thing momentarily.