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

Peter Zijlstra
2019-01-23T18:59:40Z

On Wed, Jan 23, 2019 at 02:14:26PM +0000, Patrick Bellasi wrote:

> > > Consider also that the uclamp_task_update_active() added by this patch
> > > not only has lower overhead but it will be use also by cgroups where
> > > we want to force update all the tasks on a cgroup's clamp change.
> >
> > I haven't gotten that far; but I would prefer not to have two different
> > 'change' paths in __sched_setscheduler().
>
> Yes, I agree that two paths in __sched_setscheduler() could be
> confusing. Still we have to consider that here we are adding
> "not class specific" attributes.

But that change thing is not class specific; the whole:

rq = task_rq_lock(p, &rf);
queued = task_on_rq_queued(p);
running = task_current(rq, p);
if (queued)
dequeue_task(rq, p, queue_flags);
if (running)
put_prev_task(rq, p);

/* @p is in it's invariant state; frob it's state */

if (queued)
enqueue_task(rq, p, queue_flags);
if (running)
set_curr_task(rq, p);
task_rq_unlock(rq, p, &rf);

pattern is all over the place; it is just because C sucks that that
isn't more explicitly shared (do_set_cpus_allowed(), rt_mutex_setprio(),
set_user_nice(), __sched_setscheduler(), sched_setnuma(),
sched_move_task()).

This is _the_ pattern for changing state and is not class specific at
all.