On 06/07/16 10:44, Luca Abeni wrote: > On Tue, 5 Jul 2016 17:58:30 +0100 > Juri Lelli <juri.le...@arm.com> wrote: > > > On 05/07/16 12:47, Steven Rostedt wrote: > > > On Tue, 5 Jul 2016 15:39:33 +0100 > > > Juri Lelli <juri.le...@arm.com> wrote: > > > > > > return; > > > > > > > > > > > > /* > > > > > > + * Use the scheduling parameters of the top > > > > > > pi-waiter task, > > > > > > + * if we have one from which we can inherit a > > > > > > deadline. > > > > > > + */ > > > > > > + if (pi_task && dl_se->dl_boosted && > > > > > > dl_prio(pi_task->normal_prio)) > > > > > > + pi_se = &pi_task->dl; > > > > > > + > > > > > > > > > > OK, I'm micro-optimizing now, but hey, isn't this a fast path? > > > > > > > > > > What about changing the above to: > > > > > > > > > > struct task_struct *pi_task; > > > > > [...] > > > > > > > > > > if (dl_se->dl_boosted && dl_prio(pi_task->normal_prio > > > > > && > > > > ^ > > > > OK, we need to reorder these two > > > > V > > > > > (pi_task = rt_mutex_get_top_task(dl_task_of(dl_se))) > > > > > pe_se = &pi_task->dl; > > > > > > Opps, you're right. > > > > > > > > > > > > > This way we don't need to do any work of looking at > > > > > rt_mutex_get_top_task() for the normal case. > > > > > > > > > > > > > But, yes. Looks good to me. I'll shoot a v3 ASAP. > > > > > > I have to ask, should there be any check if the dl_se has a shorter > > > deadline than the pi one? > > > > > > > Yeah. I wondered the same actually. I convinced myself that, since the > > task is boosted, we assume that the donor will have a shorter > > deadline. > > Do you mean relative deadline (dl_se->dl_deadline) or absolute > (scheduling) dealine (dl_se->deadline)? > > If I understand well, here we are in setup_new_dl_entity(), right? > This should be called only from switched_to_dl(); so, dl_se is from a > task that is switching to -deadline. If it is dl_boosted, it means that > it is switching from SCHED_OTHER (or RT) to -deadline because of > inheritance... So, it is very likely that dl_se->dl_deadline is not > meaningful. >
Right, very same thought I also had (and forgot to mention). So, we cannot really do here the check Steve was wondering about. > Moreover, setup_new_dl_entity() is only called if the current > scheduling deadline of the task is not usable (that is, if > "dl_time_before(p->dl.deadline, rq_clock(rq)"). So, dl_se->deadline > will be surely smaller than pi_se->deadline... But the inheritance has > to happen anyway. > > > > We seem to be doing the same elsewhere, but Luca was saying > > some time ago that the DI thing my have some problems and needs to be > > revised. > > My doubts regarding the inheritance code currently used for -deadline > tasks are due to the fact that it is not clear which kind of > inheritance algorithm is used... > I think it should use deadline inheritance, that, AFAIK, says that when > task T1 block waiting for task T2, T2 can inherit T1's _absolute_ > deadline - if it is earlier than T2's one. > But the current code seems to be using relative deadlines (dl_deadline) > to decide the inheritance... > True. Problem is however that, even if enforcing is disabled for a boosted task, we keep postponing the task's deadline when it depletes its runtime (soft-CBS). So, which one should we use to do so? At the instant of time the task gets a new potential donor this donor might have a shorter absolute deadline. But the task's relative deadline might be better (shorter w.r.t. donor's relative) to postpone the absolute one when needed. > Having a better look at this is in my TODO list... But I still need to > find some time :) > Same here. No spare cycles right now to have a thorough look at this. :( Thanks, - Juri
