Re: [PATCH v6 05/16] sched/core: uclamp: Update CPU's refcount on clamp changes

Peter Zijlstra
2019-01-24T12:38:14Z

On Thu, Jan 24, 2019 at 11:21:53AM +0000, Patrick Bellasi wrote:

> When a task-specific uclamp value is changed for a task, instead, a
> dequeue/enqueue is not needed. As long as we are doing a lazy update,
> that sounds just like not necessary overhead.

When that overhead is shown to be a problem, is when we'll look at that
:-)

> However, there could still be value in keeping code consistent and if
> you prefer it this way what should I do?
>
> ---8<---
> __sched_setscheduler()
> ...
> if (policy < 0)
> policy = oldpolicy = p->policy;
> ...
> if (unlikely(policy == p->policy)) {
> ...
> if (uclamp_changed()) // Force dequeue/enqueue
> goto change;
> }
> change:
> ...
>
> if (queued)
> dequeue_task(rq, p, queue_flags);
> if (running)
> put_prev_task(rq, p);
>
> __setscheduler_uclamp();
> __setscheduler(rq, p, attr, pi);
>
> if (queued)
> enqueue_task(rq, p, queue_flags);
> if (running)
> set_curr_task(rq, p);
> ...
> ---8<---
>
> Could be something like that ok with you?

Yes, that's about what I was expecting.

> Not sure about side-effects on p->prio(): for CFS seems to be reset to
> NORMAL in this case :/

That's what we need KEEP_PARAM for, right?