Messages in this thread | | | Date | Mon, 27 Apr 2020 16:17:15 +0200 | From | luca abeni <> | Subject | Re: [PATCH v2 6/6] sched/deadline: Implement fallback mechanism for !fit case |
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Hi Juri,
On Mon, 27 Apr 2020 15:34:38 +0200 Juri Lelli <juri.lelli@redhat.com> wrote:
> Hi, > > On 27/04/20 10:37, Dietmar Eggemann wrote: > > From: Luca Abeni <luca.abeni@santannapisa.it> > > > > When a task has a runtime that cannot be served within the > > scheduling deadline by any of the idle CPU (later_mask) the task is > > doomed to miss its deadline. > > > > This can happen since the SCHED_DEADLINE admission control > > guarantees only bounded tardiness and not the hard respect of all > > deadlines. In this case try to select the idle CPU with the largest > > CPU capacity to minimize tardiness. > > > > Signed-off-by: Luca Abeni <luca.abeni@santannapisa.it> > > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> [...] > > - if (!cpumask_empty(later_mask)) > > - return 1; > > + if (cpumask_empty(later_mask)) > > + cpumask_set_cpu(max_cpu, later_mask); > > Think we touched upon this during v1 review, but I'm (still?) > wondering if we can do a little better, still considering only free > cpus. > > Can't we get into a situation that some of the (once free) big cpus > have been occupied by small tasks and now a big task enters the > system and it only finds small cpus available, were it could have fit > into bigs if small tasks were put onto small cpus? > > I.e., shouldn't we always try to best fit among free cpus?
Yes; there was an additional patch that tried schedule each task on the slowest core where it can fit, to address this issue. But I think it will go in a second round of patches.
Luca
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