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Date: Wed, 17 Aug 2022 17:08:10 +0200
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Chengming Zhou <zhouchengming@...edance.com>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/9] sched/fair: fix another detach on unattached task
corner case
On Wed, 17 Aug 2022 at 17:04, Chengming Zhou
<zhouchengming@...edance.com> wrote:
>
> On 2022/8/17 23:01, Vincent Guittot wrote:
> > On Mon, 8 Aug 2022 at 14:58, Chengming Zhou <zhouchengming@...edance.com> wrote:
> >>
> >> commit 7dc603c9028e ("sched/fair: Fix PELT integrity for new tasks")
> >> fixed two load tracking problems for new task, including detach on
> >> unattached new task problem.
> >>
> >> There still left another detach on unattached task problem for the task
> >> which has been woken up by try_to_wake_up() and waiting for actually
> >> being woken up by sched_ttwu_pending().
> >>
> >> try_to_wake_up(p)
> >> cpu = select_task_rq(p)
> >> if (task_cpu(p) != cpu)
> >> set_task_cpu(p, cpu)
> >> migrate_task_rq_fair()
> >> remove_entity_load_avg() --> unattached
> >> se->avg.last_update_time = 0;
> >> __set_task_cpu()
> >> ttwu_queue(p, cpu)
> >> ttwu_queue_wakelist()
> >> __ttwu_queue_wakelist()
> >>
> >> task_change_group_fair()
> >> detach_task_cfs_rq()
> >> detach_entity_cfs_rq()
> >> detach_entity_load_avg() --> detach on unattached task
> >> set_task_rq()
> >> attach_task_cfs_rq()
> >> attach_entity_cfs_rq()
> >> attach_entity_load_avg()
> >>
> >> The reason of this problem is similar, we should check in detach_entity_cfs_rq()
> >> that se->avg.last_update_time != 0, before do detach_entity_load_avg().
> >>
> >> This patch move detach/attach_entity_cfs_rq() functions up to be together
> >> with other load tracking functions to avoid to use another #ifdef CONFIG_SMP.
> >>
> >> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
> >> ---
> >> kernel/sched/fair.c | 132 +++++++++++++++++++++++---------------------
> >> 1 file changed, 68 insertions(+), 64 deletions(-)
> >>
> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> >> index f52e7dc7f22d..4bc76d95a99d 100644
> >> --- a/kernel/sched/fair.c
> >> +++ b/kernel/sched/fair.c
> >> @@ -874,9 +874,6 @@ void init_entity_runnable_average(struct sched_entity *se)
> >> void post_init_entity_util_avg(struct task_struct *p)
> >> {
> >> }
> >> -static void update_tg_load_avg(struct cfs_rq *cfs_rq)
> >> -{
> >> -}
> >> #endif /* CONFIG_SMP */
> >>
> >> /*
> >> @@ -3176,6 +3173,7 @@ void reweight_task(struct task_struct *p, int prio)
> >> load->inv_weight = sched_prio_to_wmult[prio];
> >> }
> >>
> >> +static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
> >> static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
> >>
> >> #ifdef CONFIG_FAIR_GROUP_SCHED
> >> @@ -4086,6 +4084,71 @@ static void remove_entity_load_avg(struct sched_entity *se)
> >> raw_spin_unlock_irqrestore(&cfs_rq->removed.lock, flags);
> >> }
> >>
> >> +#ifdef CONFIG_FAIR_GROUP_SCHED
> >> +/*
> >> + * Propagate the changes of the sched_entity across the tg tree to make it
> >> + * visible to the root
> >> + */
> >> +static void propagate_entity_cfs_rq(struct sched_entity *se)
> >> +{
> >> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> +
> >> + if (cfs_rq_throttled(cfs_rq))
> >> + return;
> >> +
> >> + if (!throttled_hierarchy(cfs_rq))
> >> + list_add_leaf_cfs_rq(cfs_rq);
> >> +
> >> + /* Start to propagate at parent */
> >> + se = se->parent;
> >> +
> >> + for_each_sched_entity(se) {
> >> + cfs_rq = cfs_rq_of(se);
> >> +
> >> + update_load_avg(cfs_rq, se, UPDATE_TG);
> >> +
> >> + if (cfs_rq_throttled(cfs_rq))
> >> + break;
> >> +
> >> + if (!throttled_hierarchy(cfs_rq))
> >> + list_add_leaf_cfs_rq(cfs_rq);
> >> + }
> >> +}
> >> +#else
> >> +static void propagate_entity_cfs_rq(struct sched_entity *se) { }
> >> +#endif
> >> +
> >> +static void detach_entity_cfs_rq(struct sched_entity *se)
> >> +{
> >> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> +
> >> + /*
> >> + * In case the task sched_avg hasn't been attached:
> >> + * - A forked task which hasn't been woken up by wake_up_new_task().
> >> + * - A task which has been woken up by try_to_wake_up() but is
> >> + * waiting for actually being woken up by sched_ttwu_pending().
> >> + */
> >> + if (!se->avg.last_update_time)
> >> + return;
> >
> > The 2 lines above and the associated comment are the only relevant
> > part of the patch, aren't they ?
> > Is everything else just code moving from one place to another one
> > without change ?
>
> Yes, everything else is just code movement.
Could you remove such code movement ? It doesn't add any value to the
patch, does it ? But It makes the patch quite difficult to review and
I wasted a lot of time looking for what really changed in the code
Thanks
>
> Thanks!
>
> >
> >> +
> >> + /* Catch up with the cfs_rq and remove our load when we leave */
> >> + update_load_avg(cfs_rq, se, 0);
> >> + detach_entity_load_avg(cfs_rq, se);
> >> + update_tg_load_avg(cfs_rq);
> >> + propagate_entity_cfs_rq(se);
> >> +}
> >> +
> >> +static void attach_entity_cfs_rq(struct sched_entity *se)
> >> +{
> >> + struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> +
> >> + /* Synchronize entity with its cfs_rq */
> >> + update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
> >> + attach_entity_load_avg(cfs_rq, se);
> >> + update_tg_load_avg(cfs_rq);
> >> + propagate_entity_cfs_rq(se);
> >> +}
> >> +
> >> static inline unsigned long cfs_rq_runnable_avg(struct cfs_rq *cfs_rq)
> >> {
> >> return cfs_rq->avg.runnable_avg;
> >> @@ -4308,11 +4371,8 @@ static inline void update_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *s
> >> }
> >>
> >> static inline void remove_entity_load_avg(struct sched_entity *se) {}
> >> -
> >> -static inline void
> >> -attach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
> >> -static inline void
> >> -detach_entity_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) {}
> >> +static inline void detach_entity_cfs_rq(struct sched_entity *se) {}
> >> +static inline void attach_entity_cfs_rq(struct sched_entity *se) {}
> >>
> >> static inline int newidle_balance(struct rq *rq, struct rq_flags *rf)
> >> {
> >> @@ -11519,62 +11579,6 @@ static inline bool vruntime_normalized(struct task_struct *p)
> >> return false;
> >> }
> >>
> >> -#ifdef CONFIG_FAIR_GROUP_SCHED
> >> -/*
> >> - * Propagate the changes of the sched_entity across the tg tree to make it
> >> - * visible to the root
> >> - */
> >> -static void propagate_entity_cfs_rq(struct sched_entity *se)
> >> -{
> >> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> -
> >> - if (cfs_rq_throttled(cfs_rq))
> >> - return;
> >> -
> >> - if (!throttled_hierarchy(cfs_rq))
> >> - list_add_leaf_cfs_rq(cfs_rq);
> >> -
> >> - /* Start to propagate at parent */
> >> - se = se->parent;
> >> -
> >> - for_each_sched_entity(se) {
> >> - cfs_rq = cfs_rq_of(se);
> >> -
> >> - update_load_avg(cfs_rq, se, UPDATE_TG);
> >> -
> >> - if (cfs_rq_throttled(cfs_rq))
> >> - break;
> >> -
> >> - if (!throttled_hierarchy(cfs_rq))
> >> - list_add_leaf_cfs_rq(cfs_rq);
> >> - }
> >> -}
> >> -#else
> >> -static void propagate_entity_cfs_rq(struct sched_entity *se) { }
> >> -#endif
> >> -
> >> -static void detach_entity_cfs_rq(struct sched_entity *se)
> >> -{
> >> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> -
> >> - /* Catch up with the cfs_rq and remove our load when we leave */
> >> - update_load_avg(cfs_rq, se, 0);
> >> - detach_entity_load_avg(cfs_rq, se);
> >> - update_tg_load_avg(cfs_rq);
> >> - propagate_entity_cfs_rq(se);
> >> -}
> >> -
> >> -static void attach_entity_cfs_rq(struct sched_entity *se)
> >> -{
> >> - struct cfs_rq *cfs_rq = cfs_rq_of(se);
> >> -
> >> - /* Synchronize entity with its cfs_rq */
> >> - update_load_avg(cfs_rq, se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
> >> - attach_entity_load_avg(cfs_rq, se);
> >> - update_tg_load_avg(cfs_rq);
> >> - propagate_entity_cfs_rq(se);
> >> -}
> >> -
> >> static void detach_task_cfs_rq(struct task_struct *p)
> >> {
> >> struct sched_entity *se = &p->se;
> >> --
> >> 2.36.1
> >>
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