linux-kernel - Re: [PATCH 4/6] sched/fair: Name utilization related data and functions consistently

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Message-ID: <55F302EB.9020307@arm.com>
Date:	Fri, 11 Sep 2015 17:35:55 +0100
From:	Dietmar Eggemann <dietmar.eggemann@....com>
To:	Vincent Guittot <vincent.guittot@...aro.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Yuyang Du <yuyang.du@...el.com>,
	Michael Turquette <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	Sai Charan Gurrappadi <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] sched/fair: Name utilization related data and
 functions consistently

On 04/09/15 10:08, Vincent Guittot wrote:
> On 14 August 2015 at 18:23, Morten Rasmussen <morten.rasmussen@....com> wrote:
>> From: Dietmar Eggemann <dietmar.eggemann@....com>
>>
>> Use the advent of the per-entity load tracking rewrite to streamline the
>> naming of utilization related data and functions by using
>> {prefix_}util{_suffix} consistently. Moreover call both signals
>> ({se,cfs}.avg.util_avg) utilization.
> 
> I don't have a strong opinion about the naming of this variable but I
> remember a discussion about this topic:
> https://lkml.org/lkml/2014/9/11/474 : "Call the pure running number
> 'utilization' and this scaled with capacity 'usage' "
> 
> The utilization has been shorten to util with the rewrite of the pelt,
> so the current use of usage in get_cpu_usage still follows this rule.

But since we now do the capacity scaling in __update_load_avg()

util_sum += t * scale_freq/SCHED_CAP_SCALE * arch_scale_freq_capacity()

util_avg = util_sum / LOAD_AVG_MAX;

we could either name everything 'util' or everything 'usage' (including
the utilization sum and avg in struct sched_avg).

> 
> So why do you want to change that now ?
> Furthermore, cfs.avg.util_avg is a load  whereas sgs->group_util is a
> capacity. Both don't use the same unit and same range which can be
> confusing when you read the code

[...]

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