Messages in this thread | | | Date | Tue, 21 Mar 2023 12:13:06 +0100 | Subject | Re: [PATCH v2] sched/fair: sanitize vruntime of entity being migrated | From | Dietmar Eggemann <> |
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On 21/03/2023 11:49, Peter Zijlstra wrote: > On Tue, Mar 21, 2023 at 11:29:13AM +0100, Dietmar Eggemann wrote: >> On 21/03/2023 11:02, Peter Zijlstra wrote: >>> On Fri, Mar 17, 2023 at 05:08:10PM +0100, Vincent Guittot wrote: >>>> Commit 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed") >>>> fixes an overflowing bug, but ignore a case that se->exec_start is reset >>>> after a migration. >>>> >>>> For fixing this case, we delay the reset of se->exec_start after >>>> placing the entity which se->exec_start to detect long sleeping task. >>>> >>>> In order to take into account a possible divergence between the clock_task >>>> of 2 rqs, we increase the threshold to around 104 days. >>>> >>>> >>>> Fixes: 829c1651e9c4 ("sched/fair: sanitize vruntime of entity being placed") >>>> Signed-off-by: Zhang Qiao <zhangqiao22@huawei.com> >>>> Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> >>>> --- >>> >>> Blergh, this just isn't going to be nice. I'll go queue this for >>> sched/urgent and then we can forget about this for a little while. >>> >>> Thanks! >> >> Don't we miss setting `se->exec_start = 0` for fair task in >> move_queued_task()? ( ... and __migrate_swap_task()) >> >> https://lkml.kernel.org/r/df2cccda-1550-b06b-aa74-e0f054e9fb9d@arm.com > > Ah, I see what you mean now... When I read your and Vincent's replies > earlier today I though you mean to avoid the extra ENQUEUE_MIGRATED use, > but your actual goal was to capure more sites. > > Hmm, we could of course go add more ENQUEUE_MIGRATED, but you're right > in that TASK_ON_RQ_MIGRATING already captures that.
And in case of move_queued_task() this would have to be conditioned on SCHED_NORMAL.
> An alternative is something like the below, that matches > deactivate_task(), but still uses ENQUEUE_MIGRATED to pass it down into > the class methods. > > Hmm? > > > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2084,6 +2084,9 @@ static inline void dequeue_task(struct r > > void activate_task(struct rq *rq, struct task_struct *p, int flags) > { > + if (task_on_rq_migrating(p)) > + flags |= ENQUEUE_MIGRATED; > + > enqueue_task(rq, p, flags); > > p->on_rq = TASK_ON_RQ_QUEUED; > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8726,7 +8726,7 @@ static void attach_task(struct rq *rq, s > lockdep_assert_rq_held(rq); > > WARN_ON_ONCE(task_rq(p) != rq); > - activate_task(rq, p, ENQUEUE_NOCLOCK | ENQUEUE_MIGRATED); > + activate_task(rq, p, ENQUEUE_NOCLOCK); > check_preempt_curr(rq, p, 0); > }
Would work too.
IMHO, setting `se->exec_start = 0` for task_on_rq_migrating(p) already in migrate_task_rq_fair() would have the charm that entity_is_long_sleeper() would bail out early for these tasks.
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