On Fri, 8 May 2020 at 17:12, Tao Zhou <zohooou...@zoho.com.cn> wrote: > > Hi Phil, > > On Thu, May 07, 2020 at 04:36:12PM -0400, Phil Auld wrote: > > sched/fair: Fix enqueue_task_fair warning some more > > > > The recent patch, fe61468b2cb (sched/fair: Fix enqueue_task_fair warning) > > did not fully resolve the issues with the rq->tmp_alone_branch != > > &rq->leaf_cfs_rq_list warning in enqueue_task_fair. There is a case where > > the first for_each_sched_entity loop exits due to on_rq, having incompletely > > updated the list. In this case the second for_each_sched_entity loop can > > further modify se. The later code to fix up the list management fails to do > > what is needed because se no longer points to the sched_entity which broke > > out of the first loop. > > > > > Address this by calling leaf_add_rq_list if there are throttled parents > > while > > doing the second for_each_sched_entity loop. > > Thanks for your trace imformation and explanation. I > truely have learned from this and that. > > s/leaf_add_rq_list/list_add_leaf_cfs_rq/ > > > > > Suggested-by: Vincent Guittot <vincent.guit...@linaro.org> > > Signed-off-by: Phil Auld <pa...@redhat.com> > > Cc: Peter Zijlstra (Intel) <pet...@infradead.org> > > Cc: Vincent Guittot <vincent.guit...@linaro.org> > > Cc: Ingo Molnar <mi...@kernel.org> > > Cc: Juri Lelli <juri.le...@redhat.com> > > --- > > kernel/sched/fair.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 02f323b85b6d..c6d57c334d51 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -5479,6 +5479,13 @@ enqueue_task_fair(struct rq *rq, struct task_struct > > *p, int flags) > > /* end evaluation on encountering a throttled cfs_rq */ > > if (cfs_rq_throttled(cfs_rq)) > > goto enqueue_throttle; > > + > > + /* > > + * One parent has been throttled and cfs_rq removed from the > > + * list. Add it back to not break the leaf list. > > + */ > > + if (throttled_hierarchy(cfs_rq)) > > + list_add_leaf_cfs_rq(cfs_rq); > > } > > I was confused by why the throttled cfs rq can be on list. > It is possible when enqueue a task and thanks to the 'threads'. > But I think the above comment does not truely put the right > intention, right ? > If throttled parent is onlist, the child cfs_rq is ignored > to be added to the leaf cfs_rq list me think. > > unthrottle_cfs_rq() follows the same logic if i am not wrong. > Is it necessary to add the above to it ?
When a cfs_rq is throttled, its sched group is dequeued and all child cfs_rq are removed from leaf_cfs_rq list. But the sched group of the child cfs_rq stay enqueued in the throttled cfs_rq so child sched group->on_rq might be still set. > > Thanks, > Tau > > > > > enqueue_throttle: > > -- > > 2.18.0 > > > > V2 rework the fix based on Vincent's suggestion. Thanks Vincent. > > > > > > Cheers, > > Phil > > > > -- > >
