Messages in this thread | | | Date | Wed, 15 Apr 2020 15:20:04 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH 3/4] sched/deadline: Make DL capacity-aware |
| |
On 15/04/20 11:39, Dietmar Eggemann wrote: > On 10.04.20 14:52, Juri Lelli wrote: > > Hi, > > > > On 08/04/20 11:50, Dietmar Eggemann wrote: > >> From: Luca Abeni <luca.abeni@santannapisa.it> > > [...] > > >> @@ -1623,10 +1624,19 @@ select_task_rq_dl(struct task_struct *p, int cpu, int sd_flag, int flags) > >> * other hand, if it has a shorter deadline, we > >> * try to make it stay here, it might be important. > >> */ > >> - if (unlikely(dl_task(curr)) && > >> - (curr->nr_cpus_allowed < 2 || > >> - !dl_entity_preempt(&p->dl, &curr->dl)) && > >> - (p->nr_cpus_allowed > 1)) { > >> + select_rq = unlikely(dl_task(curr)) && > >> + (curr->nr_cpus_allowed < 2 || > >> + !dl_entity_preempt(&p->dl, &curr->dl)) && > >> + p->nr_cpus_allowed > 1; > >> + > >> + /* > >> + * We take into account the capacity of the CPU to > >> + * ensure it fits the requirement of the task. > >> + */ > >> + if (static_branch_unlikely(&sched_asym_cpucapacity)) > >> + select_rq |= !dl_task_fits_capacity(p, cpu); > > > > I'm thinking that, while dl_task_fits_capacity() works well when > > selecting idle cpus, in this case we should consider the fact that curr > > might be deadline as well and already consuming some of the rq capacity. > > > > Do you think we should try to take that into account, maybe using > > dl_rq->this_bw ? > > So you're saying that cpudl_find(..., later_mask) could return 1 (w/ > best_cpu (cp->elements[0].cpu) in later_mask). > > And that this best_cpu could be a non-fitting CPU for p. > > This could happen if cp->free_cpus is empty (no idle CPUs) so we take > cpudl_find()'s else path and in case p's deadline < cp->elements[0] > deadline. > > We could condition the 'return 1' on best_cpu fitting p. > > But should we do this for cpudl_find(..., NULL) calls from > check_preempt_equal_dl() as well or will this break GEDF?
So, even by not returning best_cpu, as above, if it doesn't fit p's bw requirement, I think we would be breaking GEDF, which however doesn't take asym capacities into account. OTOH, if we let p migrate to a cpu that can't suit it, it will still be missing its deadlines (plus it would be causing deadline misses on the task that was running on best_cpu).
check_preempt_equal_dl() worries me less, as it is there to service corner cases (hopefully not so frequent).
| |