On Thu, Feb 11, 2016 at 12:24:29PM +0000, Juri Lelli wrote:
> Hi Peter,
>
> On 11/02/16 12:59, Peter Zijlstra wrote:
> > On Tue, Feb 09, 2016 at 05:02:33PM -0800, Steve Muckle wrote:
> > > > Index: linux-pm/kernel/sched/deadline.c
> > > > ===================================================================
> > > > --- linux-pm.orig/kernel/sched/deadline.c
> > > > +++ linux-pm/kernel/sched/deadline.c
> > > > @@ -1197,6 +1197,9 @@ static void task_tick_dl(struct rq *rq,
> > > > {
> > > > update_curr_dl(rq);
> > > >
> > > > + /* Kick cpufreq to prevent it from stalling. */
> > > > + cpufreq_kick();
> > > > +
> > > > /*
> > > > * Even when we have runtime, update_curr_dl() might have
> > > > resulted in us
> > > > * not being the leftmost task anymore. In that case
> > > > NEED_RESCHED will
> > >
> > > I think additional hooks such as enqueue/dequeue would be needed in
> > > RT/DL. The task tick callbacks will only run if a task in that class is
> > > executing at the time of the tick. There could be intermittent RT/DL
> > > task activity in a frequency domain (the only task activity there, no
> > > CFS tasks) that doesn't happen to overlap the tick. Worst case the task
> > > activity could be periodic in such a way that it never overlaps the tick
> > > and the update is never made.
> >
> > No, for RT (RR/FIFO) we do not have enough information to do anything
> > useful. Basically RR/FIFO should result in running 100% whenever we
> > schedule such a task.
> >
> > That means RR/FIFO want a hook in pick_next_task_rt() to bump the freq
> > to 100% and leave it there until something else gets to run.
> >
>
> Vincent is trying to play with rt_avg (in the last sched-freq thread) to
> see if we can get some information about RT as well. I understand that
> from a theoretical perspective that's not much we can say of such tasks,
> and bumping to max can be the only sensible thing to do, but there are
> users of RT (ehm, Android) that will probably see differences in energy
> consumption if we do so. Yeah, maybe the should use a different policy,
> yes.
Can't we just leave broken people get broken results? Trying to use
rt_avg for this is just insane. We should ensure that people using this
thing correctly get correct results, the rest can take a hike.
Using rt_avg gets us to the place where people who want to do the right
thing cannot, and that is bad.
> > For DL it basically wants to set a minimum freq based on reserved
> > utilization, so that is __setparam_dl() or somewhere around there.
> >
>
> I think we could do better than this once Luca's reclaiming stuff gets
> in. The reserved bw is usually somewhat pessimistic. But this is a
> different discussion, maybe.
Sure, there's cleverer things that can be done. But a simple one would
indeed be the min guarantee based on accepted bandwidth.
