Re: [Patch v4 4/6] sched/fair: update cpu_capcity to reflect thermal pressure

Qais Yousef
2019-10-31T10:53:50Z

On 10/28/19 16:30, Peter Zijlstra wrote:
> On Wed, Oct 23, 2019 at 01:28:40PM +0100, Qais Yousef wrote:
> > On 10/22/19 16:34, Thara Gopinath wrote:
> > > cpu_capacity relflects the maximum available capacity of a cpu. Thermal
> > > pressure on a cpu means this maximum available capacity is reduced. This
> > > patch reduces the average thermal pressure for a cpu from its maximum
> > > available capacity so that cpu_capacity reflects the actual
> > > available capacity.
> > >
> > > Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> > > ---
> > > kernel/sched/fair.c | 1 +
> > > 1 file changed, 1 insertion(+)
> > >
> > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > > index 4f9c2cb..be3e802 100644
> > > --- a/kernel/sched/fair.c
> > > +++ b/kernel/sched/fair.c
> > > @@ -7727,6 +7727,7 @@ static unsigned long scale_rt_capacity(struct sched_domain *sd, int cpu)
> > >
> > > used = READ_ONCE(rq->avg_rt.util_avg);
> > > used += READ_ONCE(rq->avg_dl.util_avg);
> > > + used += READ_ONCE(rq->avg_thermal.load_avg);
> >
> > Maybe a naive question - but can we add util_avg with load_avg without
> > a conversion? I thought the 2 signals have different properties.
>
> Changelog of patch #1 explains, it's in that dense blob of text.
>
> But yes, you're quite right that that wants a comment here.

Thanks for the pointer! A comment would be nice indeed.

To make sure I got this correctly - it's because avg_thermal.load_avg
represents delta_capacity which is already a 'converted' form of load. So this
makes avg_thermal.load_avg a util_avg really. Correct?

If I managed to get it right somehow. It'd be nice if we can do inverse
conversion on delta_capacity so that avg_thermal.{load_avg, util_avg} meaning
is consistent across the board. But I don't feel strongly about it if this gets
documented properly.

Thanks

--
Qais Yousef