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

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Message-ID: <20161116152605.GU3142@twins.programming.kicks-ass.net>
Date:   Wed, 16 Nov 2016 16:26:05 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rafael Wysocki <rjw@...ysocki.net>, 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 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>