Re: [PATCH] sched/core: use correct cpu_capacity in wake_affine_weight()

[Honglei Wang]

On 2022/11/16 19:00, Vincent Guittot wrote:
> On Wed, 16 Nov 2022 at 10:12, Honglei Wang <wanghonglei@xxxxxxxxxxxxxx> wrote:
> > It seems make more sense to do the load weight calculation with
> > respective cpu_capacity.
> >
> > Signed-off-by: Honglei Wang <wanghonglei@xxxxxxxxxxxxxx>
> > ---
> >   kernel/sched/fair.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index e4a0b8bd941c..a9f75040969b 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -6262,13 +6262,13 @@ wake_affine_weight(struct sched_domain *sd, struct task_struct *p,
> >          this_eff_load += task_load;
> >          if (sched_feat(WA_BIAS))
> >                  this_eff_load *= 100;
> > -       this_eff_load *= capacity_of(prev_cpu);
> > +       this_eff_load *= capacity_of(this_cpu);
> >
> >          prev_eff_load = cpu_load(cpu_rq(prev_cpu));
> >          prev_eff_load -= task_load;
> >          if (sched_feat(WA_BIAS))
> >                  prev_eff_load *= 100 + (sd->imbalance_pct - 100) / 2;
> > -       prev_eff_load *= capacity_of(this_cpu);
> > +       prev_eff_load *= capacity_of(prev_cpu);
>
> we want to test :
>      (cpu_load(this_rq) + task_h_load(p) ) / capacity_of(this_cpu)  <
> cpu_load(prev_rq) / capacity_of(prev_cpu)
>
> but instead of doing expensive division, we do the below which gives
> the same result
>      (cpu_load(this_rq) + task_h_load(p) ) * capacity_of(prev_cpu)  <
> cpu_load(prev_rq) * capacity_of(this_cpu)

ha, I misunderstand the strategy, thanks for coaching, Vincent.

> >          /*
> >           * If sync, adjust the weight of prev_eff_load such that if
> > --
> > 2.14.1