Re: [PATCH 4/4] sched: fix wakeup preemption

[Chris Friesen]

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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