Messages in this thread | | | Date | Mon, 22 Jun 2015 19:18:05 +0100 | From | Dietmar Eggemann <> | Subject | Re: [PATCH v8 1/4] sched: Remove rq's runnable avg |
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On 21/06/15 23:26, Yuyang Du wrote: > Hi Dietmar, > > On Fri, Jun 19, 2015 at 07:27:24PM +0100, Dietmar Eggemann wrote: >> Hi Yuyang, >> >> On 15/06/15 20:26, Yuyang Du wrote: >>> The current rq->avg is not used at all since its merge into kernel, >>> and the code is in the scheduler's hot path, so remove it. >> >> are you sure that this is the case? I was always under the impression >> that w/ CONFIG_FAIR_GROUP_SCHED=y rq->avg (runnable_avg_sum, avg_period) >> is used to calculate contrib in __update_tg_runnable_avg() for the root >> group (cfs_rq->tg->css.id = 1). >> >> On tg's w/ cfs_rq->tg->css.id > 1, se->avg (runnable_avg_sum, >> avg_period) is used instead but we simply don't have a tg related se for >> the root group. IMHO, that's why we have this rq::avg. > > Yes, I agree. But the root group's avg is not useful anyway. If it is, > we sure should keep it.
You're right. Both consumers of tg->load_avg and tg->runnable_avg (__update_group_entity_contrib() and calc_tg_weight()) are never called w/ cfs_rq->tg->css.id < 2 .
I did some tests w/ task groups on my ARM platform. The system survives an appropriate BUG_ON in both functions just fine.
Maybe you can put a little bit more information why rq::avg isn't needed even in the CONFIG_FAIR_GROUP_SCHED=y case into the patch header?
I assume getting rid of extra code in the current per-entity load-tracking code is a good thing. And this patch is probably less complicated to understand than your second one :-)
> >> I understand that w/ the second patch in your series you don't need >> rq::avg any more. > > And the rq->avg can be replaced by the root cfs_rq's util_avg, too.
Given the fact that it is not used this wouldn't be necessary.
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