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SubjectRe: [PATCH] sched/core: use correct cpu_capacity in wake_affine_weight()
On Wed, 16 Nov 2022 at 10:12, Honglei Wang <wanghonglei@didiglobal.com> wrote:
>
> It seems make more sense to do the load weight calculation with
> respective cpu_capacity.
>
> Signed-off-by: Honglei Wang <wanghonglei@didiglobal.com>
> ---
> 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)


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

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