Messages in this thread | | | Subject | Re: [RFC 0/12][PATCH] SCHED_DEADLINE: core of the scheduling class | From | Dario Faggioli <> | Date | Wed, 13 Jan 2010 17:32:21 +0100 |
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On Tue, 2009-12-29 at 15:30 +0100, Peter Zijlstra wrote: > On Fri, 2009-10-16 at 17:40 +0200, Raistlin wrote: > > +struct task_struct *pick_next_task_deadline(struct rq *rq) > > +{ > > + struct sched_dl_entity *dl_se; > > + struct task_struct *p; > > + struct dl_rq *dl_rq; > > + > > + dl_rq = &rq->dl; > > + > > + if (likely(!dl_rq->dl_nr_running)) > > + return NULL; > > + > > + dl_se = pick_next_deadline_entity(rq, dl_rq); > > + BUG_ON(!dl_se); > > + > > + p = deadline_task_of(dl_se); > > + p->se.exec_start = rq->clock; > > +#ifdef CONFIG_SCHED_HRTICK > > + if (hrtick_enabled(rq)) > > + start_hrtick_deadline(rq, p); > > +#endif > > + return p; > > +} > > I'm not sure about actually using hrtick like this, I'd expect > SCHED_DEADLINE to always use hrtimers when available. The only reason > to use some of the hrtick infrastructure is to re-use the hrtick_start() > logic which uses IPIs to ensure we program the timer on the right cpu > (so we can schedule from it). > Yeah, that and the fact that it seemed to me very easy and clean to: - check for runtime enforcement inside the task_tick_deadline function, as other scheduling classes do, and then - if possible, ask that task_tick_deadline function to be called right at the time instant I expect my runtime to be depleted. If that won't happen --because of no-hrtick or no-hires-hrtimers-- the check will still be performed during the next tick.
> The whole IPI mess requires USE_GENERIC_SMP_HELPERS, which makes > CONFIG_HRTICK useful (ensures we have hrtimers enabled and have generic > IPI bits) > > The problem is that things like hrtick_enabled() also check > sched_feat(HRTICK) which is disabled by default (because programming the > clock hw on each schedule was found too expensive) but that should not > stop SCHED_DEADLINE from using it. > Mmm... I might have lost you here... :-(
Do you think that keep using hrtick_start and alike, even if sched_feat(HRTICK) is disabled, could be good enough? Or are you suggesting something different? IOTH, should I simply bypass the sched_feat()/hrtick_enabled() check or you think I need something more?
Thanks and regards, Dario
-- <<This happens because I choose it to happen!>> (Raistlin Majere) ---------------------------------------------------------------------- Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy)
http://blog.linux.it/raistlin / raistlin@ekiga.net / dario.faggioli@jabber.org [unhandled content-type:application/pgp-signature] | |