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SubjectRe: [PATCH 4/4] sched: fix wakeup preemption
Peter Zijlstra wrote:

> In my recent wakeup preempt rework I messed up the asym wakeup.
> The idea is that it should be easier to preempt lighter tasks
> but not harder to preempt heavier tasks.

> Index: linux-2.6/kernel/sched_fair.c
> ===================================================================
> --- linux-2.6.orig/kernel/sched_fair.c
> +++ linux-2.6/kernel/sched_fair.c
> @@ -1243,8 +1243,8 @@ static unsigned long wakeup_gran(struct
> * More easily preempt - nice tasks, while not making it harder for
> * + nice tasks.
> */
> - if (sched_feat(ASYM_GRAN))
> - gran = calc_delta_mine(gran, NICE_0_LOAD, &se->load);
> + if (sched_feat(ASYM_GRAN) && se->load.weight < NICE_0_LOAD)
> + gran = (gran * se->load.weight) >> NICE_0_SHIFT;
>
> return gran;
> }

Setting aside whether the asym wakeup is desirable, the code looks
reasonable but I think you need to change the code comments as well.

The proposed code only affects with a weight of less than NICE_0_LOAD,
ie. +nice tasks. The comment suggests the opposite.

Chris


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