linux-kernel - Re: [PATCH] sched: put rq's sched_avg under CONFIG_FAIR_GROUP

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Date:	Tue, 25 Feb 2014 17:47:11 +0000
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
CC:	Peter Zijlstra <peterz@...radead.org>,
	Ben Segall <bsegall@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched: put rq's sched_avg under CONFIG_FAIR_GROUP_SCHED

On 25/02/14 13:16, Srikar Dronamraju wrote:
>> The struct sched_avg of struct rq is only used in case group
>> scheduling is enabled inside __update_tg_runnable_avg() to update
>> per-cpu representation of a task group.  I.e. that there is no need to
>> maintain the runnable avg of a rq in the !CONFIG_FAIR_GROUP_SCHED case.
>>
>> This patch guards struct sched_avg of struct rq and
>> update_rq_runnable_avg() with CONFIG_FAIR_GROUP_SCHED.
>>
> 
> While this patch looks good, I see fields in sched_avg viz decay_count,
> last_runnable_update, load_avg_contrib  only relevant to sched_entity.
> i.e they don't seem to be updated or used for rq->avg. Should we look at
> splitting sched_avg so that rq->avg doesn't have unwanted fields?

Yes, AFAICS at least load_avg_contrib and decay_count are only relevant
for struct sched_entity whereas last_runnable_update is used in
__update_entity_runnable_avg() itself.

By having struct sched_avg embedded into struct sched_entity and struct
rq, __update_entity_runnable_avg() and __update_tg_runnable_avg() can be
used on both and moreover, all current members of struct sched_avg
belong logically together.

With this patch I was more interested in the fact that we do not have to
maintain the load avg for struct rq in a !CONFIG_FAIR_GROUP_SCHED system.

-- Dietmar

> 
> --
> Thanks and Regards
> Srikar Dronamraju
> 
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