On 4 July 2017 at 10:34, Peter Zijlstra <[email protected]> wrote: > On Tue, Jul 04, 2017 at 09:27:07AM +0200, Peter Zijlstra wrote: >> On Sat, Jul 01, 2017 at 07:06:13AM +0200, Vincent Guittot wrote: >> > The running state is a subset of runnable state which means that running >> > can't be set if runnable (weight) is cleared. There are corner cases >> > where the current sched_entity has been already dequeued but cfs_rq->curr >> > has not been updated yet and still points to the dequeued sched_entity. >> > If ___update_load_avg is called at that time, weight will be 0 and running >> > will be set which is not possible. >> > >> > This case happens during pick_next_task_fair() when a cfs_rq becomes idles. >> > The current sched_entity has been dequeued so se->on_rq is cleared and >> > cfs_rq->weight is null. But cfs_rq->curr still points to se (it will be >> > cleared when picking the idle thread). Because the cfs_rq becomes idle, >> > idle_balance() is called and ends up to call update_blocked_averages() >> > with these wrong running and runnable states. >> > >> > Add a test in ___update_load_avg to correct the running state in this case. >> >> Cute, however did you find that ? > > Hmm,.. could you give a little more detail? > > Because if ->on_rq=0, we'll have done dequeue_task() which will have > done update_curr() with ->on_rq, weight and ->running consistently. > > Then the above, inconsistent update should not happen, because delta=0.
In fact, the delta between dequeue_entity_load_avg() and update_blocked_averages() is not 0 on my platform (hikey) but can be longer than 60us (at lowest frequency with only 1 task group level)
