Messages in this thread | | | Date | Fri, 12 May 2017 22:58:09 +0200 | From | luca abeni <> | Subject | Re: [PATCH v2 2/3] sched/deadline: Throttle the task when missing its deadline |
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On Fri, 12 May 2017 15:19:55 +0800 Xunlei Pang <xpang@redhat.com> wrote: [...] > >> "As seen, enforcing that the total utilization is smaller than M > >> does not guarantee that global EDF schedules the tasks without > >> missing any deadline (in other words, global EDF is not an optimal > >> scheduling algorithm). However, a total utilization smaller than M > >> is enough to guarantee that non real-time tasks are not starved > >> and that the tardiness of real-time tasks has an upper bound[12] > >> (as previously noted). Different bounds on the maximum tardiness > >> experienced by real-time tasks have been developed in various > >> papers[13,14], but the theoretical result that is important for > >> SCHED_DEADLINE is that if the total utilization is smaller or equal > >> than M then the response times of the tasks are limited." > >> > >> Do you mean there is some tardiness allowed in theory(global EDF is > >> not an optimal scheduling algorithm), thus missed deadline is > >> allowed for global EDF? > > Right. > > > > With the admission test currently used by the kernel (sum of > > utilizations <= 1), tasks are guaranteed to have a tardiness smaller > > than a theoretical maximum... But this theoretical maximum can be > > larger than 0. > > > > If you want to strictly respect all of the deadlines, you need a > > stricter admission test (for example, the one based on WCET_max > > that is mentioned above). > > Understood. > > I think in Patch 3, it is still worthy to add the accounting in > dl_runtime_exceeded(), to track the dl scheduling tardiness(after all > tardiness is not a good thing) like: if > (dl_time_before(dl_se->deadline, rq_clock(rq)) && dl_se->runtime > 0) > ++dl_se->nr_underrun_sched; > > Maybe changing the name to use "nr_underrun_tardy" is better, large > value does need our attention. What do you think?
I do not know, I never used statistics like these...
If there are enough people having a good usecase for these statistics, it might be worth adding them, but I do not know other people's opinions about this.
Luca
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