Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 6 Mar 2020 08:59:06 +0100 | Subject | Re: [PATCH v2] sched/fair : fix reordering of enqueue_task_fair |
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On Thu, 5 Mar 2020 at 19:39, <bsegall@google.com> wrote: > > Vincent Guittot <vincent.guittot@linaro.org> writes: > > > Even when a cgroup is throttled, the group se of a child cgroup can still > > be enqueued and its gse->on_rq stays true. When a task is enqueued on such > > child, we still have to update the load_avg and increase > > h_nr_running of the throttled cfs. Nevertheless, the 1st > > for_each_sched_entity loop is skipped because of gse->on_rq == true and the > > 2nd loop because the cfs is throttled whereas we have to update both > > load_avg with the old h_nr_running and increase h_nr_running in such case. > > Note that the update of load_avg will effectively happen only once in order > > to sync up to the throttled time. Next call for updating load_avg will stop > > early because the clock stays unchanged. > > > > Fixes: 6d4d22468dae ("sched/fair: Reorder enqueue/dequeue_task_fair path") > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > --- > > kernel/sched/fair.c | 8 ++++---- > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index fcc968669aea..5b232d261842 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5431,16 +5431,16 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > for_each_sched_entity(se) { > > cfs_rq = cfs_rq_of(se); > > > > - /* end evaluation on encountering a throttled cfs_rq */ > > - if (cfs_rq_throttled(cfs_rq)) > > - goto enqueue_throttle; > > - > > update_load_avg(cfs_rq, se, UPDATE_TG); > > se_update_runnable(se); > > update_cfs_group(se); > > > > cfs_rq->h_nr_running++; > > cfs_rq->idle_h_nr_running += idle_h_nr_running; > > + > > + /* end evaluation on encountering a throttled cfs_rq */ > > + if (cfs_rq_throttled(cfs_rq)) > > + goto enqueue_throttle; > > } > > > > enqueue_throttle: > > > I think there's an equivalent issue on dequeue as well, though that's > much rarer to trigger (but still possible). I think the same fix works > there too?
I thought it was not needed because we don't have the "if (se->on_rq) break" in dequeue but : /* Avoid re-evaluating load for this entity: */ se = parent_entity(se); It creates similar behavior for the parent
I'm going to add it. Thanks
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