Re: [PATCH v2 1/5] sched/fair: Reorder enqueue/dequeue_task_fair path

[Dietmar Eggemann]

On 18/02/2020 15:15, Vincent Guittot wrote:
> On Tue, 18 Feb 2020 at 14:22, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>>
>> On Tue, Feb 18, 2020 at 01:37:37PM +0100, Dietmar Eggemann wrote:
>>> On 14/02/2020 16:27, Vincent Guittot wrote:
>>>> The walk through the cgroup hierarchy during the enqueue/dequeue of a task
>>>> is split in 2 distinct parts for throttled cfs_rq without any added value
>>>> but making code less readable.
>>>>
>>>> Change the code ordering such that everything related to a cfs_rq
>>>> (throttled or not) will be done in the same loop.
>>>>
>>>> In addition, the same steps ordering is used when updating a cfs_rq:
>>>> - update_load_avg
>>>> - update_cfs_group
>>>> - update *h_nr_running
>>>
>>> Is this code change really necessary? You pay with two extra goto's. We
>>> still have the two for_each_sched_entity(se)'s because of 'if
>>> (se->on_rq); break;'.
>>
>> IIRC he relies on the presented ordering in patch #5 -- adding the
>> running_avg metric.
> 
> Yes, that's the main reason, updating load_avg before h_nr_running

My hunch is you refer to the new function:

static inline void se_update_runnable(struct sched_entity *se)
{
        if (!entity_is_task(se))
                se->runnable_weight = se->my_q->h_nr_running;
}

I don't see the dependency to the 'update_load_avg -> h_nr_running'
order since it operates on se->my_q, not cfs_rq = cfs_rq_of(se), i.e.
se->cfs_rq.

What do I miss here?