linux-kernel - Re: [PATCH 2/5] cpufreq: schedutil: support scheduler cpufreq callbacks on remote CPUs

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Message-ID: <20160519225939.GA15383@graphite.smuckle.net>
Date:	Thu, 19 May 2016 15:59:39 -0700
From:	Steve Muckle <steve.muckle@...aro.org>
To:	"Rafael J. Wysocki" <rafael@...nel.org>
Cc:	Steve Muckle <steve.muckle@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Juri Lelli <Juri.Lelli@....com>,
	Patrick Bellasi <patrick.bellasi@....com>,
	Michael Turquette <mturquette@...libre.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [PATCH 2/5] cpufreq: schedutil: support scheduler cpufreq
 callbacks on remote CPUs

On Thu, May 19, 2016 at 10:55:23PM +0200, Rafael J. Wysocki wrote:
> >> > +static inline bool sugov_queue_remote_callback(struct sugov_policy *sg_policy,
> >> > +                                        int cpu)
> >> > +{
> >> > +       struct cpufreq_policy *policy = sg_policy->policy;
> >> > +
> >> > +       if (!cpumask_test_cpu(smp_processor_id(), policy->cpus)) {
> >>
> >> This check is overkill for policies that aren't shared (and we have a
> >> special case for them already).
> >
> > I don't see why it is overkill -
> 
> Because it requires more computation, memory accesses etc than simply
> comparing smp_processor_id() with cpu.

Do you have a preference on how to restructure this? Otherwise I'll
create a second version of sugov_update_commit, factoring out as much of
it as I can into two inline sub-functions. 

...
> 
> > but it seems like an odd inconsistency for the governor to trace unchanged
> > frequencies when fast switches are enabled but not otherwise. It'd be
> > useful I think for profiling and tuning if the tracing was consistent.
> 
> Well, fair enough.
> 
> > This behavioral change is admittedly not part of the purpose of the
> > patch and could be split out if needbe.
> 
> No need to split IMO, but it might be prudent to mention that change
> in behavior in the changelog.

Will do.

thanks,
Steve