Re: [PATCH] cpufreq: Avoid unnecessary frequency updates due to mismatch

[Rafael J. Wysocki]

On Thu, May 5, 2022 at 3:32 PM Matthias Brugger <matthias.bgg@xxxxxxxxx> wrote:
>
>
>
> On 04/05/2022 10:21, Viresh Kumar wrote:
> > For some platforms, the frequency returned by hardware may be slightly
> > different from what is provided in the frequency table. For example,
> > hardware may return 499 MHz instead of 500 MHz. In such cases it is
> > better to avoid getting into unnecessary frequency updates, as we may
> > end up switching policy->cur between the two and sending unnecessary
> > pre/post update notifications, etc.
> >
> > This patch has chosen allows the hardware frequency and table frequency
> > to deviate by 1 MHz for now, we may want to increase it a bit later on
> > if someone still complains.
> >
> > Reported-by: Rex-BC Chen <rex-bc.chen@xxxxxxxxxxxx>
> > Signed-off-by: Viresh Kumar <viresh.kumar@xxxxxxxxxx>
>
> Reviewed-by: Matthias Brugger <matthias.bgg@xxxxxxxxx>
>
> > ---
> >   drivers/cpufreq/cpufreq.c | 11 +++++++++++
> >   1 file changed, 11 insertions(+)
> >
> > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> > index 0d58b0f8f3af..233e8af48848 100644
> > --- a/drivers/cpufreq/cpufreq.c
> > +++ b/drivers/cpufreq/cpufreq.c
> > @@ -28,6 +28,7 @@
> >   #include <linux/suspend.h>
> >   #include <linux/syscore_ops.h>
> >   #include <linux/tick.h>
> > +#include <linux/units.h>
> >   #include <trace/events/power.h>
> >
> >   static LIST_HEAD(cpufreq_policy_list);
> > @@ -1708,6 +1709,16 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b
> >               return new_freq;
> >
> >       if (policy->cur != new_freq) {
> > +             /*
> > +              * For some platforms, the frequency returned by hardware may be
> > +              * slightly different from what is provided in the frequency
> > +              * table, for example hardware may return 499 MHz instead of 500
> > +              * MHz. In such cases it is better to avoid getting into
> > +              * unnecessary frequency updates.
> > +              */
> > +             if (abs(policy->cur - new_freq) < HZ_PER_MHZ)
> > +                     return policy->cur;
> > +
> >               cpufreq_out_of_sync(policy, new_freq);
> >               if (update)
> >                       schedule_work(&policy->update);

Applied as 5.19 material, thanks!