Hi Dmitry, Did you see this behaviour or is this an analysis of the code? On Tue, 22 Apr 2008, Dmitry Adamushko wrote: > > consider the following 2-cpu system: cpu0 and cpu1. > > cpu0: is idle --> in such a state, it never pulls RT tasks on its own. > > T0 and T1 are RT tasks This is the important part. How did cpu0 get to "is idle --> in such a state, it never pulls RT tasks on its own" ? And then have cpu1 have T0 and T1 running. When ever a cpu goes to idle, it should definitely try to do a RT pull before going idle. When a > > > square#0: > > cpu1: T0 is running > > T1 is of the same prio as T0 (shouldn't really matter but to get the > same result it would require altering the flow of events slightly) > > T1's affinity allows it to be run only on cpu1. > T0 can run on both. > > try_to_wake_up() is called for T1. > | > --> select_task_rq_rt() => gives cpu1 > | > --> task_wake_up_rt() > | > ---> push_rt_tasks() -> rq->rt.pushed = 1 > > now, neither T1 (due to its affinity), nor T0 (it's running) can be > pushed away to cpu0. Ah, this may be what you are talking about. T0 was running, but because T1 has its affinity set to cpu1 it wont cause a push. When T0 schedules away to give T1 its cpu time, T0 wont push away because of the pushed flag. Hmm, interesting. Of course my response is "Don't use SCHED_RR! It's evil!" ;-) Perhaps we need logic to reset the push flag when a sched RR task is scheduled out to give way for another SCHED_RR task. This should fix this scenario. Unless I'm missing something else. -- Steve > [ btw., (1) I'd expect that this task_wake_up_rt() thing should be > redundant, logically-wise... I'll check once more and comment later > on. > (2) any example when (p->prio >= rq->rt.highest_prio) is not true in > task_wake_up_rt() ? > ] > > as a result, rq->rt.pushed == 1. > > Now, post_schedule_rt() won't call push_rt_tasks(). > > T0 and T1 are both running for some time on cpu1 (possibly > context-switching if they are both of SCHED_RR type). > > Then they both block, _first_ T1 and then T0. > > After some interval of time, they wake up (let's say they are > periodic) in the following order: _first_ T0 and then T1. > > rq->rt.pushed becomes 0 and here we are back to square#0. The whole > story repeats again. > > cpu0 is idle so it won't pull T0. Both T0 and T1 are competing for the > same cpu. Not good. > > am I missing smth? > > > -- > Best regards, > Dmitry Adamushko > -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
