Re: [PATCH V2] sched: fair: Use the earliest break even

[Vincent Guittot]

On Fri, 13 Mar 2020 at 14:17, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote:
>
> On 13/03/2020 14:15, Vincent Guittot wrote:
> > On Fri, 13 Mar 2020 at 13:15, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote:
>
> [ ... ]
>
> >>>>>> +
> >>>>>> +       if (idle_state)
> >>>>>> +               idle_set_break_even(rq, ktime_get_ns() +
> >>>>>
> >>>>> What worries me a bit is that it adds one ktime_get call each time a
> >>>>> cpu enters idle
> >>>>
> >>>> Right, we can improve this in the future by folding the local_clock() in
> >>>> cpuidle when entering idle with this ktime_get.
> >>>
> >>> Using local_clock() would be more latency friendly
> >>
> >> Unfortunately we are comparing the deadline across CPUs, so the
> >> local_clock() can not be used here.
> >>
> >> But if we have one ktime_get() instead of a local_clock() + ktime_get(),
> >> that should be fine, no?
> >
> > Can't this computation of break_even be done in cpuidle framework
> > while computing other statistics for selecting the idle state instead
> > ? cpuidle already uses ktime_get for next hrtimer as an example.
> > So cpuidle compute break_even and make it available to scheduler like
> > exit_latency. And I can imagine that system wide time value will also
> > be needed when looking at next wakeup event of cluster/group of CPUs
>
> Ok, so you suggest to revisit and consolidate the whole time capture in
> cpuidle? I think that makes sense.

Yes

>
>
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