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Message-ID: <fa2e11fc-5a49-b88a-1daa-ad6e5f5dea51@bytedance.com>
Date: Wed, 17 Aug 2022 23:04:09 +0800
From: Chengming Zhou <zhouchengming@...edance.com>
To: Vincent Guittot <vincent.guittot@...aro.org>
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 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.
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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