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

[Peter Zijlstra]

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?