Messages in this thread | | | From | Vincent Guittot <> | Date | Thu, 20 Feb 2020 11:31:23 +0100 | Subject | Re: [PATCH] sched/fair: add !se->on_rq check before dequeue entity |
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On Thu, 20 Feb 2020 at 11:09, chenqiwu <qiwuchen55@gmail.com> wrote: > > On Thu, Feb 20, 2020 at 10:38:02AM +0100, Vincent Guittot wrote: > > On Thu, 20 Feb 2020 at 08:29, <qiwuchen55@gmail.com> wrote: > > > > > > From: chenqiwu <chenqiwu@xiaomi.com> > > > > > > We igonre checking for !se->on_rq condition before dequeue one > > > entity from cfs rq. It must be required in case the entity has > > > been dequeued. > > > > Do you have a use case that triggers this situation ? > > > > This is the only way to reach this situation seems to be dequeuing a > > task on a throttled cfs_rq > > > Sorry, I have no use case triggers this situation. It's just found by > reading code. > I agree the situation you mentioned above may have a racy with > dequeue_task_fair() in the following code path: > __schedule > pick_next_task_fair > put_prev_entity > check_cfs_rq_runtime > throttle_cfs_rq > dequeue_entity > > So this check is worth to be added for dequeue_task_fair().
In fact the check is already done thanks to the: if (cfs_rq_throttled(cfs_rq)) AFAICT, there is no other way to enqueue a task on a cfs_rq for which the group entity is not enqueued
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