Re: [PATCH V2 1/4] cpufreq: stats: Defer stats update to cpufreq_stats_record_transition()

[Rafael J. Wysocki]

On Fri, Sep 25, 2020 at 12:58 PM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 25-09-20, 12:04, Rafael J. Wysocki wrote:
> > I'm actually wondering if reset_time is necessary at all.
> >
> > If cpufreq_stats_record_transition() is the only updater of the stats,
> > which will be the case after applying this series IIUC, it may as well
> > simply set the new starting point and discard all of the data
> > collected so far if reset_pending is set.
> >
> > IOW, the time when the reset has been requested isn't particularly
> > relevant IMV (and it is not exact anyway), because the user is
> > basically asking for discarding "history" and that may very well be
> > interpreted to include the current sample.
>
> There are times when this would be visible to userspace and won't look nice.
>
> Like, set governor to performance, reset the stats and after 10 seconds, read
> the stats again, everything will be 0.

Unless I'm missing something, the real reset happens when
cpufreq_stats_record_transition() runs next time, so the old stats
will still be visible at that point, won't they?

> Because cpufreq_stats_record_transition()
> doesn't get called at all here, we would never clear them until the time
> governor is changed and so we need to keep a track of reset-time.

Or trigger a forced update.