Re: [PATCH v4 5/5] sched: add two functions for att(det)aching a task to(from) a cfs_rq

Byungchul Park
2015-09-01T00:28:54Z

On Mon, Aug 31, 2015 at 05:21:38PM +0200, Peter Zijlstra wrote:
> On Thu, Aug 20, 2015 at 08:35:16PM +0900, Byungchul Park wrote:
> > On Thu, Aug 20, 2015 at 08:22:00PM +0900, byungchul.park@lge.com wrote:
>
> > > + /*
> > > + * If it's !queued, then only when the task is sleeping it has a
> > > + * non-normalized vruntime, that is, when the task is being migrated
> > > + * it has a normailized vruntime.
> > > + */
> >
> > i tried to change your XXX comment. i think it can be explaned like this.
> > don't you think so? i want to hear any opinions about this.
> >
> > > + if (p->state == TASK_RUNNING)
> > > + return true;
>
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -7943,11 +7943,10 @@ static inline bool vruntime_normalized(s
> return true;
>
> /*
> - * If it's !queued, then only when the task is sleeping it has a
> - * non-normalized vruntime, that is, when the task is being migrated
> - * it has a normalized vruntime.
> + * If it's !queued, sleeping tasks have a normalized vruntime,
> + * see dequeue_entity().

check the condition "!(flags & DEQUEUE_SLEEP)" for doing normalizing in
dequeue_entity(). i think you have to keep my original comment, or
modify your comment to something like below.

before - If it's !queued, sleeping tasks have a normalized vruntime,
after - If it's !queued, sleeping tasks have a non-normalize vruntime,

but.. i think it would be better that you keep my original comment..

> */
> - if (p->state == TASK_RUNNING)
> + if (!p->se.on_rq)
> return true;
>
> return false;
>
>
> Does that make sense?
>
> I think using p->state for this is fragile, as we could be racy with any
> random blocking primitive that does set_current_state() _before_
> actually calling into the scheduler.
>
>
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