Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 14 Feb 2020 08:42:38 +0100 | Subject | Re: [RFC 3/4] sched/fair: replace runnable load average by runnable average |
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On Wed, 12 Feb 2020 at 15:30, Mel Gorman <mgorman@suse.de> wrote: > > On Tue, Feb 11, 2020 at 06:46:50PM +0100, Vincent Guittot wrote: > > Now that runnable_load_avg is not more used, we can replace it by a new > > signal that will highlight the runnable pressure on a cfs_rq. This signal > > track the waiting time of tasks on rq and can help to better define the > > state of rqs. > > > > At now, only util_avg is used to define the state of a rq: > > A rq with more that around 80% of utilization and more than 1 tasks is > > considered as overloaded. > > > > But the util_avg signal of a rq can become temporaly low after that a task > > migrated onto another rq which can bias the classification of the rq. > > > > When tasks compete for the same rq, their runnable average signal will be > > higher than util_avg as it will include the waiting time and we can use > > this signal to better classify cfs_rqs. > > > > The new runnable_avg will track the runnable time of a task which simply > > adds the waiting time to the running time. The runnbale _avg of cfs_rq > > will be the /Sum of se's runnable_avg and the runnable_avg of group entity > > will follow the one of the rq similarly to util_avg. > > > > s/runnbale/runnable/ > > Otherwise, all I can do is give a heads-up that I will not be able to > review this patch and the next patch properly in the short-term. While the > new metric appears to have a sensible definition, I've not spent enough > time comparing/contrasting the pro's and con's of PELT implementation > details or their consequences. I am not confident I can accurately > predict whether this is better or if there are corner cases that make > poor placement decisions based on fast changes of runnable_avg. At least > not within a reasonable amount of time.
ok. understood
> > This caught my attention though > > > @@ -4065,8 +4018,8 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags) > > * - Add its new weight to cfs_rq->load.weight > > */ > > update_load_avg(cfs_rq, se, UPDATE_TG | DO_ATTACH); > > + se_update_runnable(se); > > update_cfs_group(se); > > - enqueue_runnable_load_avg(cfs_rq, se); > > account_entity_enqueue(cfs_rq, se); > > > > if (flags & ENQUEUE_WAKEUP) > > I don't think the ordering matters any more because of what was removed > from update_cfs_group. Unfortunately, I'm not 100% confident so am > bringing it to your attention in case it does.
Yes. I have just tried to keep the same order with se_update_runnable() just below update_load_avg() like for other places
> > -- > Mel Gorman > SUSE Labs
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