linux-kernel - Re: [PATCH V2 1/3] Calculate Thermal Pressure

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Date:   Thu, 25 Apr 2019 14:45:57 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Quentin Perret <quentin.perret@....com>
Cc:     Thara Gopinath <thara.gopinath@...aro.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Zhang Rui <rui.zhang@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Amit Kachhap <amit.kachhap@...il.com>,
        viresh kumar <viresh.kumar@...aro.org>,
        Javi Merino <javi.merino@...nel.org>,
        Eduardo Valentin <edubezval@...il.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Nicolas Dechesne <nicolas.dechesne@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>
Subject: Re: [PATCH V2 1/3] Calculate Thermal Pressure

On Thu, 25 Apr 2019 at 12:57, Quentin Perret <quentin.perret@....com> wrote:
>
> On Tuesday 16 Apr 2019 at 15:38:39 (-0400), Thara Gopinath wrote:
> > +/* Per cpu structure to keep track of Thermal Pressure */
> > +struct thermal_pressure {
> > +     unsigned long scale; /* scale reflecting average cpu max capacity*/
> > +     unsigned long acc_scale; /* Accumulated scale for this time window */
> > +     unsigned long old_scale; /* Scale value for the previous window */
> > +     unsigned long raw_scale; /* Raw max capacity */
> > +     unsigned long age_stamp; /* Last time old_scale was updated */
> > +     unsigned long last_update; /* Last time acc_scale was updated */
> > +     spinlock_t lock; /* Lock for protecting from simultaneous access*/
> > +     /* Timer for periodic update of thermal pressure */
> > +     struct timer_list timer;
>
> Do you actually need the periodic update ? You only really need to
> update the 'scale' value when updating the LB stats no ? Nobody
> accesses that value in between two LBs.

Do you mean calling a variant of sched_update_thermal_pressure() in
update_cpu_capacity() instead of periodic update ?
Yes , that should be enough

>
> Thanks,
> Quentin