Messages in this thread | | | From | Vincent Guittot <> | Date | Wed, 19 Feb 2020 17:26:11 +0100 | Subject | Re: [PATCH v2 1/5] sched/fair: Reorder enqueue/dequeue_task_fair path |
| |
On Wed, 19 Feb 2020 at 12:07, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote: > > On 18/02/2020 15:15, Vincent Guittot wrote: > > On Tue, 18 Feb 2020 at 14:22, Peter Zijlstra <peterz@infradead.org> 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?
update_load_avg() updates both se and cfs_rq so if you update cfs_rq->h_nr_running before calling update_load_avg() like in the 2nd for_each_sched_entity, you will update cfs_rq runnable_avg for the past time slot with the new h_nr_running value instead of the previous value.
| |