Re: [RFC PATCH 3/4] sched/fair: delay update_tg_load_avg() for cfs_rq's removed load

[Vincent Guittot <vincent.guittot@linaro.org>]

On Thu, 20 Jul 2023 at 17:22, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:
>
> On 20/07/2023 17:02, Vincent Guittot wrote:
> > On Thu, 20 Jul 2023 at 16:42, Aaron Lu <aaron.lu@intel.com> wrote:
> >>
> >> On Thu, Jul 20, 2023 at 03:10:30PM +0200, Vincent Guittot wrote:
> >>> On Wed, 19 Jul 2023 at 15:29, Aaron Lu <aaron.lu@intel.com> wrote:
> >>>>
> >>>> On Wed, Jul 19, 2023 at 11:47:06AM +0200, Vincent Guittot wrote:
> >>>>> On Wed, 19 Jul 2023 at 10:01, Aaron Lu <aaron.lu@intel.com> wrote:
> >>>>>>
> >>>>>> On Wed, Jul 19, 2023 at 01:18:26PM +0800, Aaron Lu wrote:
>
> [...]
>
> > What was wrong with your proposal to limit the update inside
> > update_tg_load_avg()  ? except maybe s/1000000/NSEC_PER_MSEC/ and
> > computing delta after testing the time since last update
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index a80a73909dc2..e48fd0e6982d 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -3665,6 +3665,7 @@ static inline bool cfs_rq_is_decayed(struct
> > cfs_rq *cfs_rq)
> >  static inline void update_tg_load_avg(struct cfs_rq *cfs_rq)
> >  {
> >         long delta = cfs_rq->avg.load_avg - cfs_rq->tg_load_avg_contrib;
> > +       u64 now = cfs_rq_clock_pelt(cfs_rq);
>
> Could this be `u64 now = sched_clock_cpu()` like in
> migrate_se_pelt_lag() or newidle_balance() to avoid the time morphing
> due to PELT's frequency and uArch invariance?

yes that's a good point. I missed this

> >
> >         /*
> >          * No need to update load_avg for root_task_group as it is not used.
>
> [...]
>