linux-kernel - Re: [PATCH v4 7/7] cpufreq: schedutil: New governor based on scheduler utilization data

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Message-ID: <3401840.ChzILGGFZI@vostro.rjw.lan>
Date:	Wed, 16 Mar 2016 23:53:47 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v4 7/7] cpufreq: schedutil: New governor based on scheduler utilization data

On Wednesday, March 16, 2016 11:40:54 PM Peter Zijlstra wrote:
> On Wed, Mar 16, 2016 at 10:38:55PM +0100, Rafael J. Wysocki wrote:
> > On Wednesday, March 16, 2016 07:14:20 PM Peter Zijlstra wrote:
> > > On Wed, Mar 16, 2016 at 03:59:18PM +0100, Rafael J. Wysocki wrote:
> > > > +static void sugov_update_commit(struct sugov_policy *sg_policy, u64 time,
> > > > +				unsigned int next_freq)
> > > > +{
> > > > +	struct cpufreq_policy *policy = sg_policy->policy;
> > > > +
> > > > +	if (next_freq > policy->max)
> > > > +		next_freq = policy->max;
> > > > +	else if (next_freq < policy->min)
> > > > +		next_freq = policy->min;
> > > > +
> > > > +	sg_policy->last_freq_update_time = time;
> > > > +	if (sg_policy->next_freq == next_freq) {
> > > > +		if (policy->fast_switch_enabled)
> > > > +			trace_cpu_frequency(policy->cur, smp_processor_id());
> > > > +
> > > > +		return;
> > > > +	}
> > > > +
> > > > +	sg_policy->next_freq = next_freq;
> > > > +	if (policy->fast_switch_enabled) {
> > > > +		unsigned int freq;
> > > > +
> > > > +		freq = cpufreq_driver_fast_switch(policy, next_freq);
> > > 
> > > So you're assuming a RELATION_L for ->fast_switch() ?
> > 
> > Yes, I am.
> 
> Should we document that fact somewhere? Or alternatively, if you already
> did, I simply missed it.

I thought I did, but clearly that's not the case (I think I wrote about that
in a changelog comments somewhere).

I'll document it in the kerneldoc for cpufreq_driver_fast_switch() (patch [6/7]).