Re: [patch 08/18] sched: add support for throttling group entities

Peter Zijlstra
2011-08-08T16:00:53Z

On Mon, 2011-08-08 at 23:46 +0800, Lin Ming wrote:
> On Fri, Jul 22, 2011 at 12:43 AM, Paul Turner <pjt@google.com> wrote:
>
> > +static __used void throttle_cfs_rq(struct cfs_rq *cfs_rq)
> > +{
> > + struct rq *rq = rq_of(cfs_rq);
> > + struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
> > + struct sched_entity *se;
> > + long task_delta, dequeue = 1;
> > +
> > + se = cfs_rq->tg->se[cpu_of(rq_of(cfs_rq))];
> > +
> > + /* account load preceding throttle */
> > + update_cfs_load(cfs_rq, 0);
> > +
> > + task_delta = cfs_rq->h_nr_running;
> > + for_each_sched_entity(se) {
> > + struct cfs_rq *qcfs_rq = cfs_rq_of(se);
> > + /* throttled entity or throttle-on-deactivate */
> > + if (!se->on_rq)
> > + break;
>
> Does it mean it's possible that child se is unthrottled but parent se
> is throttled?

Yep..

> I thought if parent group was throttled then its children should be
> throttled too.
> I may misunderstood the code, please correct me then.

That would be costly, as throttling a parent would require throttling
all its children (of which there can be arbitrary many).