linux-kernel - Re: [PATCH v3 2/6] cpufreq: schedutil: ensure max frequency while running RT/DL tasks

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Date:   Thu, 30 Nov 2017 15:45:06 +0000
From:   Patrick Bellasi <patrick.bellasi@....com>
To:     Juri Lelli <juri.lelli@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Todd Kjos <tkjos@...roid.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle.linux@...il.com>
Subject: Re: [PATCH v3 2/6] cpufreq: schedutil: ensure max frequency while
 running RT/DL tasks

On 30-Nov 14:17, Juri Lelli wrote:
> Hi,
> 
> On 30/11/17 11:47, Patrick Bellasi wrote:
> 
> [...]
> 
> > @@ -340,6 +349,7 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> >  	struct sugov_policy *sg_policy = sg_cpu->sg_policy;
> >  	unsigned long util, max;
> >  	unsigned int next_f;
> > +	bool rt_mode;
> >  
> >  	sugov_get_util(&util, &max, sg_cpu->cpu);
> >  
> > @@ -353,17 +363,27 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> >  		sg_cpu->flags = 0;
> >  		goto done;
> >  	}
> > -	sg_cpu->flags = flags;
> > +
> > +	/*
> > +	 * 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(current) ||
> > +		  task_has_rt_policy(current) ||
> > +		  (flags & SCHED_CPUFREQ_RT_DL);
> > +	if (rt_mode)
> > +		sg_cpu->flags |= flags;
> > +	else
> > +		sg_cpu->flags = flags;
> >  
> >  	sugov_set_iowait_boost(sg_cpu, time, flags);
> >  	sg_cpu->last_update = time;
> >  
> >  	if (sugov_should_update_freq(sg_policy, time)) {
> > -		if (flags & SCHED_CPUFREQ_RT_DL)
> > -			next_f = sg_policy->policy->cpuinfo.max_freq;
> > -		else
> > -			next_f = sugov_next_freq_shared(sg_cpu, time);
> > -
> > +		next_f = rt_mode
> > +			? sg_policy->policy->cpuinfo.max_freq
> > +			: sugov_next_freq_shared(sg_cpu, time);
> >  		sugov_update_commit(sg_policy, time, next_f);
> 
> Aren't we already at max_freq at this point (since an RT/DL task is
> running)? Do we need to trigger a frequency update?

I think that's required to cover the first time we enter rt_mode in
order to jump to max OPP.

If we are already at max OPP, sugov_update_commit() will just bail out
without doing anything.

Am I missing something?

> 
> Best,
> 
> Juri

-- 
#include <best/regards.h>

Patrick Bellasi