linux-kernel - Re: [PATCH v3 3/6] cpufreq: schedutil: update CFS util only if used

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Date:   Thu, 30 Nov 2017 15:57:28 +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>
Subject: Re: [PATCH v3 3/6] cpufreq: schedutil: update CFS util only if used

On 30-Nov 14:22, Juri Lelli wrote:
> Hi,
> 
> On 30/11/17 11:47, Patrick Bellasi wrote:
> > Currently the utilization of the FAIR class is collected before locking
> > the policy. Although that should not be a big issue for most cases, we
> > also don't really know how much latency there can be between the
> > utilization reading and its usage.
> > 
> > Let's get the FAIR utilization right before its usage to be better in
> > sync with the current status of a CPU.
> > 
> > Signed-off-by: Patrick Bellasi <patrick.bellasi@....com>
> > Reviewed-by: Dietmar Eggemann <dietmar.eggemann@....com>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > Cc: Viresh Kumar <viresh.kumar@...aro.org>
> > Cc: linux-kernel@...r.kernel.org
> > Cc: linux-pm@...r.kernel.org
> > 
> > ---
> > Changes from v2:
> > - rebased on v4.15-rc1
> > 
> > Change-Id: I9291a560bcad7db76894e3f0fcdb917511d0479e
> > ---
> >  kernel/sched/cpufreq_schedutil.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
> > index 448f49de5335..40521d59630b 100644
> > --- a/kernel/sched/cpufreq_schedutil.c
> > +++ b/kernel/sched/cpufreq_schedutil.c
> > @@ -351,10 +351,9 @@ static void sugov_update_shared(struct update_util_data *hook, u64 time,
> >  	unsigned int next_f;
> >  	bool rt_mode;
> >  
> > -	sugov_get_util(&util, &max, sg_cpu->cpu);
> > -
> >  	raw_spin_lock(&sg_policy->update_lock);
> >  
> > +	sugov_get_util(&util, &max, sg_cpu->cpu);
> >  	sg_cpu->util = util;
> >  	sg_cpu->max = max;
> 
> Patch looks good.
> 
> Reviewed-by: Juri Lelli <juri.lelli@...hat.com>
> 
> However, not sure $SUBJECT is really in sync with what the patch does?
> CFS gets "used" before and after the patch... last paragraph of the
> changelog looks more like it. :)

Yes, that's a pretty trivial update with a confusing changelog.

If we think it's worth to keep (and correct as well) I'll update the
commit message.

Thanks for poinint that out.

> Best,
> 
> Juri

Cheers Patrick

-- 
#include <best/regards.h>

Patrick Bellasi