Messages in this thread | | | Date | Thu, 16 Apr 2020 15:19:38 +0200 | From | Juri Lelli <> | Subject | Re: [PATCH 3/4] sched/deadline: Make DL capacity-aware |
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On 15/04/20 18:42, luca abeni wrote: > Hi Juri, > > On Wed, 15 Apr 2020 15:20:04 +0200 > Juri Lelli <juri.lelli@redhat.com> wrote: > [...] > > > > 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. > > Well, gEDF could take asymmetric capacities into account by scheduling > the earliest deadline task on the fastest CPU (and the task with the > second earliest deadline on the second fastest CPU, and so on...) > > But this could cause a lot of unneeded migrations (I tried to discuss > this issue in a previous OSPM presentation). My original approach to > work around this issue was to schedule a task on the slowest core on > which the task can fit (some experiments revealed that this heuristic > can approximate the gEDF behaviour without causing too many > migrations)... But this patch is not included on the current patchset, > and will be proposed later, after the most important patches have been > merged.
OK, makes sense to me. And I'm ok also with a 2 steps approach. Asym idle now and asym busy with a later series.
Best,
Juri
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