Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH] nohz/full, sched/rt: Fix missed tick-reenabling bug in dequeue_task_rt | Date | Fri, 01 Jul 2022 12:25:28 +0100 |
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On 28/06/22 11:22, Nicolas Saenz Julienne wrote: > dequeue_task_rt() only decrements 'rt_rq->rt_nr_running' after having > called sched_update_tick_dependency() preventing it from re-enabling the > tick on systems that no longer have pending SCHED_RT tasks but have > multiple runnable SCHED_OTHER tasks: > > dequeue_task_rt() > dequeue_rt_entity() > dequeue_rt_stack() > dequeue_top_rt_rq() > sub_nr_running() // decrements rq->nr_running > sched_update_tick_dependency() > sched_can_stop_tick() // checks rq->rt.rt_nr_running, > ... > __dequeue_rt_entity() > dec_rt_tasks() // decrements rq->rt.rt_nr_running > ... > > Every other scheduler class performs the operation in the opposite > order, and sched_update_tick_dependency() expects the values to be > updated as such. So avoid the misbehaviour by inverting the order in > which the above operations are performed in the RT scheduler. >
I can't see anything wrong with your approach, though I did have to spend some time re-learning RT_GROUP_SCHED. The designated Fixes: commit looks about right too.
> Fixes: 76d92ac305f2 ("sched: Migrate sched to use new tick dependency mask model") > Signed-off-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
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