linux-kernel - Re: [PATCH v10 7/7] sched: Clean up load average references

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Message-ID: <55B26AC9.5040508@arm.com>
Date:	Fri, 24 Jul 2015 17:41:45 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Yuyang Du <yuyang.du@...el.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	"pjt@...gle.com" <pjt@...gle.com>,
	"bsegall@...gle.com" <bsegall@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"umgwanakikbuti@...il.com" <umgwanakikbuti@...il.com>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>
Subject: Re: [PATCH v10 7/7] sched: Clean up load average references

On 15/07/15 01:04, Yuyang Du wrote:
> For cfs_rq, we have load.weight, runnable_load_avg, and load_avg. We
> now start to clean up how they are used.
> 
> First, as group sched_entity already largely uses load_avg, we now expand
> to use load_avg in all cases.

You're talking about group se's or cfs_rq owned by the group se's
(se->my_q) here or both?

Just asking because both data structures (cfs_rq and se) have a 'struct
load_weight load' as well as 'struct sched_avg avg' member.

 Second, for CPU-wide load balancing, we
> choose to use runnable_load_avg in all cases, which is the same as before
> this series.

With your patch-set there will be still the difference of
'cfs_rq->utilization_load_avg' and your 'cfs_rq->avg.util_avg' in the
sense that the former one does not contain the contribution of blocked se's.

The EAS patch-set adds blocked utilization contribution:
https://lkml.org/lkml/2015/7/7/915

The cfs_rq utilization is also used by the load-balancer code via
get_cpu_usage() so the blocked utilization contribution to
'cfs_rq->avg.util_avg' can change load-balancing as well.

Since it is not as heavily used as the cfs_rq->runnable_load_avg we
might not need to reintroduce cfs_rq->utilization_load_avg but at least
mention this here.

-- Dietmar

[...]

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