linux-kernel - Re: [PATCH V2 3/4] cpufreq: schedutil: move slow path from workqueue to SCHED

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Message-ID: <1627825.eiM24BDMdD@vostro.rjw.lan>
Date:   Thu, 24 Nov 2016 02:19:03 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Peter Zijlstra <peterz@...radead.org>,
        Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Juri Lelli <Juri.Lelli@....com>,
        Robin Randhawa <robin.randhawa@....com>,
        Steve Muckle <smuckle.linux@...il.com>
Subject: Re: [PATCH V2 3/4] cpufreq: schedutil: move slow path from workqueue to SCHED_FIFO task

On Wednesday, November 16, 2016 04:26:05 PM Peter Zijlstra wrote:
> On Tue, Nov 15, 2016 at 01:53:22PM +0530, Viresh Kumar wrote:
> > @@ -308,7 +313,21 @@ static void sugov_irq_work(struct irq_work *irq_work)
> >  	struct sugov_policy *sg_policy;
> >  
> >  	sg_policy = container_of(irq_work, struct sugov_policy, irq_work);
> > +
> > +	/*
> > +	 * For Real Time and Deadline tasks, schedutil governor shoots the
> > +	 * frequency to maximum. And special care must be taken to ensure that
> > +	 * this kthread doesn't result in that.
> > +	 *
> > +	 * This is (mostly) guaranteed by the work_in_progress flag. The flag is
> > +	 * updated only at the end of the sugov_work() and before that schedutil
> > +	 * rejects all other frequency scaling requests.
> > +	 *
> > +	 * Though there is a very rare case where the RT thread yields right
> > +	 * after the work_in_progress flag is cleared. The effects of that are
> > +	 * neglected for now.
> > +	 */
> > +	kthread_queue_work(&sg_policy->worker, &sg_policy->work);
> >  }
> 
> 
> Right, so that's a wee bit icky, but its also entirely pre-existing
> code.
> 
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Whole series applied.

Thanks,
Rafael