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

[Vincent Guittot]

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