linux-kernel - Re: [PATCH 3/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks

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Date:   Fri, 3 Mar 2017 14:01:45 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        John Stultz <john.stultz@...aro.org>,
        Juri Lelli <juri.lelli@....com>, Todd Kjos <tkjos@...roid.com>,
        Tim Murray <timmurray@...gle.com>,
        Andres Oportus <andresoportus@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Chris Redpath <chris.redpath@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH 3/6] cpufreq: schedutil: ensure max frequency while
 running RT/DL tasks

On 02-03-17, 15:45, Patrick Bellasi wrote:
> diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> @@ -293,15 +305,29 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
>  	if (curr == sg_policy->thread)
>  		goto done;
>  
> +	/*
> +	 * While RT/DL tasks are running we do not want FAIR tasks to
> +	 * overwrite this CPU's flags, still we can update utilization and
> +	 * frequency (if required/possible) to be fair with these tasks.
> +	 */
> +	rt_mode = task_has_dl_policy(curr) ||
> +		  task_has_rt_policy(curr) ||
> +		  (flags & SCHED_CPUFREQ_RT_DL);
> +	if (rt_mode)
> +		sg_cpu->flags |= flags;
> +	else
> +		sg_cpu->flags = flags;

This looks so hacked up :)

Wouldn't it be better to let the scheduler tell us what all kind of tasks it has
in the rq of a CPU and pass a mask of flags? I think it wouldn't be difficult
(or time consuming) for the scheduler to know that, but I am not 100% sure.

IOW, the flags field in cpufreq_update_util() will represent all tasks in the
rq, instead of just the task that is getting enqueued/dequeued..

And obviously we need to get some utilization numbers for the RT and DL tasks
going forward, switching to max isn't going to work for ever :)

-- 
viresh