On 05/13/2017 at 04:58 AM, luca abeni wrote: > On Fri, 12 May 2017 15:19:55 +0800 > Xunlei Pang <xp...@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. >
Hi Luca, Thanks for the feedback. I think I can defer the statistics patch after Daniel's "sched/deadline: Use the revised wakeup rule for suspending constrained dl tasks", since there will be another underrun case in the fix, let's wait for other's opinions then. Regards, Xunlei
