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Subject: Re: [PATCH 4/6] sched/fair: Name utilization related data and
 functions consistently
To: Vincent Guittot <vincent.guittot@linaro.org>,
        Morten Rasmussen <Morten.Rasmussen@arm.com>
References: <1439569394-11974-1-git-send-email-morten.rasmussen@arm.com>
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 <CAKfTPtBUec-OobXGpWMfxXuq2s==o5LquNWGEo5Te_2Gqw1SHw@mail.gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
        "mingo@redhat.com" <mingo@redhat.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Yuyang Du <yuyang.du@intel.com>,
        Michael Turquette <mturquette@baylibre.com>,
        "rjw@rjwysocki.net" <rjw@rjwysocki.net>,
        Juri Lelli <Juri.Lelli@arm.com>,
        Sai Charan Gurrappadi <sgurrappadi@nvidia.com>,
        "pang.xunlei@zte.com.cn" <pang.xunlei@zte.com.cn>,
        linux-kernel <linux-kernel@vger.kernel.org>
From: Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <55F302EB.9020307@arm.com>
Date: Fri, 11 Sep 2015 17:35:55 +0100
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On 04/09/15 10:08, Vincent Guittot wrote:
> On 14 August 2015 at 18:23, Morten Rasmussen <morten.rasmussen@arm.com> wrote:
>> From: Dietmar Eggemann <dietmar.eggemann@arm.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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