Messages in this thread | | | From | bsegall@google ... | Subject | Re: [PATCH] sched/fair : prevent unlimited runtime on throttled group | Date | Tue, 14 Jan 2020 10:29:43 -0800 |
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Vincent Guittot <vincent.guittot@linaro.org> writes:
> When a running task is moved on a throttled task group and there is no > other task enqueued on the CPU, the task can keep running using 100% CPU > whatever the allocated bandwidth for the group and although its cfs rq is > throttled. Furthermore, the group entity of the cfs_rq and its parents are > not enqueued but only set as curr on their respective cfs_rqs. > > We have the following sequence: > > sched_move_task > -dequeue_task: dequeue task and group_entities. > -put_prev_task: put task and group entities. > -sched_change_group: move task to new group. > -enqueue_task: enqueue only task but not group entities because cfs_rq is > throttled. > -set_next_task : set task and group_entities as current sched_entity of > their cfs_rq. > > Another impact is that the root cfs_rq runnable_load_avg at root rq stays > null because the group_entities are not enqueued. This situation will stay > the same until an "external" event triggers a reschedule. Let trigger it > immediately instead.
Sounds reasonable to me, "moved group" being an explicit resched check doesn't sound like a problem in general.
> > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > --- > kernel/sched/core.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index e7b08d52db93..d0acc67336c0 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7062,8 +7062,15 @@ void sched_move_task(struct task_struct *tsk) > > if (queued) > enqueue_task(rq, tsk, queue_flags); > - if (running) > + if (running) { > set_next_task(rq, tsk); > + /* > + * After changing group, the running task may have joined a > + * throttled one but it's still the running task. Trigger a > + * resched to make sure that task can still run. > + */ > + resched_curr(rq); > + } > > task_rq_unlock(rq, tsk, &rf); > }
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