linux-kernel - Re: [PATCH 4/6 v5] sched: propagate load during synchronous attach/detach

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Date:   Wed, 26 Oct 2016 09:05:49 +0200
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Yuyang Du <yuyang.du@...el.com>,
        Morten Rasmussen <Morten.Rasmussen@....com>,
        "linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
        Paul Turner <pjt@...gle.com>, Ben Segall <bsegall@...gle.com>,
        Wanpeng Li <kernellwp@...il.com>
Subject: Re: [PATCH 4/6 v5] sched: propagate load during synchronous attach/detach

On 21 October 2016 at 14:19, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>
> On 10/17/2016 10:14 AM, Vincent Guittot wrote:
>>
>> When a task moves from/to a cfs_rq, we set a flag which is then used to
>> propagate the change at parent level (sched_entity and cfs_rq) during
>> next update. If the cfs_rq is throttled, the flag will stay pending until
>> the cfs_rw is unthrottled.
>
>
> minor nit:
>
> s/cfs_rw/cfs_rq

yes

>
> [...]
>
>
>> @@ -8704,6 +8867,22 @@ static void detach_task_cfs_rq(struct task_struct *p)
>>         update_load_avg(se, 0);
>>         detach_entity_load_avg(cfs_rq, se);
>>         update_tg_load_avg(cfs_rq, false);
>> +
>> +#ifdef CONFIG_FAIR_GROUP_SCHED
>> +       /*
>> +        * Propagate the detach across the tg tree to make it visible to the
>> +        * root
>> +        */
>> +       se = se->parent;
>> +       for_each_sched_entity(se) {
>> +               cfs_rq = cfs_rq_of(se);
>> +
>> +               if (cfs_rq_throttled(cfs_rq))
>> +                       break;
>> +
>> +               update_load_avg(se, UPDATE_TG);
>> +       }
>> +#endif
>>  }
>>
>>  static void attach_entity_cfs_rq(struct sched_entity *se)
>> @@ -8722,6 +8901,22 @@ static void attach_entity_cfs_rq(struct sched_entity *se)
>>         update_load_avg(se, sched_feat(ATTACH_AGE_LOAD) ? 0 : SKIP_AGE_LOAD);
>>         attach_entity_load_avg(cfs_rq, se);
>>         update_tg_load_avg(cfs_rq, false);
>> +
>> +#ifdef CONFIG_FAIR_GROUP_SCHED
>> +       /*
>> +        * Propagate the attach across the tg tree to make it visible to the
>> +        * root
>> +        */
>> +       se = se->parent;
>> +       for_each_sched_entity(se) {
>> +               cfs_rq = cfs_rq_of(se);
>> +
>> +               if (cfs_rq_throttled(cfs_rq))
>> +                       break;
>> +
>> +               update_load_avg(se, UPDATE_TG);
>> +       }
>> +#endif
>>  }
>
>
> The 'detach across' and 'attach across' in detach_task_cfs_rq() and attach_entity_cfs_rq() do the same so couldn't you not create a function propagate_foo() for it? This would avoid this ifdef as well.
>
> You could further create in your '[PATCH 1/6 v5] sched: factorize attach entity':
>
> detach_entity_cfs_rq() {
>   update_load_avg()
>   detach_entity_load_avg()
>   update_tg_load_avg()
>   propagate_load_avg()
> }
>
> and then we would have:
>
> attach_task_cfs_rq() -> attach_entity_cfs_rq() -> propagate_foo()
> detach_task_cfs_rq() -> detach_entity_cfs_rq() -> propagate_foo()
>
> I guess you didn't because it would be only called one time but this symmetric approaches are easier to remember (at least for me).

Yes i haven't created attach_entity_cfs_rq because it would be used only once.
Regarding the creation of a propagate_foo function, i have just
followed a similar skeleton as what is done in
enqueue/dequeue_task_fair

I don't have strong opinion about creating this indirection for code
readability. Others, have you got a preference ?

>
> [...]