Hi Juri, On 08/11/2015 01:55 PM, Juri Lelli wrote: > As you are running a 3.14 kernel, you probably missed this fix > 5bfd126e80dc "sched/deadline: Fix sched_yield() behavior". Can > you please check?
I stumbled over this commit but somehow managed to ignore it. Anyway, I upgraded to 4.1, now the application shows the expected behavior. >> As far as I understand, I have to call sched_yield() if the the >> execution time of one loop iteration is either not constant or unknown >> (both cases being very likely), because if I do not, a new loop >> iteration could be started if the time budget is not empty. >> > > It depends. The sched_yield() semantic for SCHED_DEADLINE might > be used to implement some sort of reclaiming mechanism (not > there yet) where you inform the scheduler that you are not going > to use the remaining runtime in this period; and the scheduler > could recycle this spare runtime for other tasks that are running > short of it. > > However, I'd say that in your case you can also live without it. > SCHED_DEADLINE can handle sporadic tasks, it depends on how you > implement your userspace loop I guess. If you just check the active > flag, and this flag is always set, you are right that you may > end up executing back to back, though; in which case it seems that yield > semantic could do the trick. Since samples are generated and the resulting curve looks like it was sampled with a constant frequency, I think that sched_yield() is to be used in this context. Before I used sched_yield(), I had to use some sleep statements, which made the sample frequency not deterministic and filled the CPU up. Now it seems to work pretty well. Congrats on the deadline scheduler - it is a great way to introduce some real-time capability - and thank you for your help. Best regards, Michael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/