linux-kernel - Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity

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Message-ID: <xm26wpvsucm5.fsf@sword-of-the-dawn.mtv.corp.google.com>
Date:	Mon, 14 Sep 2015 10:36:34 -0700
From:	bsegall@...gle.com
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Morten Rasmussen <morten.rasmussen@....com>,
	Peter Zijlstra <peterz@...radead.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	"mingo\@redhat.com" <mingo@...hat.com>,
	"daniel.lezcano\@linaro.org" <daniel.lezcano@...aro.org>,
	"mturquette\@baylibre.com" <mturquette@...libre.com>,
	"rjw\@rjwysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"sgurrappadi\@nvidia.com" <sgurrappadi@...dia.com>,
	"pang.xunlei\@zte.com.cn" <pang.xunlei@....com.cn>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig

Yuyang Du <yuyang.du@...el.com> writes:

> On Fri, Sep 11, 2015 at 10:05:53AM -0700, bsegall@...gle.com wrote:
>> 
>> SCHED_LOAD_RESOLUTION and the non-SLR part of SCHED_LOAD_SHIFT are not
>> required to be the same value and should not be conflated.
>  
>> In particular, since cgroups are on the same timeline as tasks and their
>> shares are not scaled by SCHED_LOAD_SHIFT in any way (but are scaled so
>> that SCHED_LOAD_RESOLUTION is invisible), changing that part of
>> SCHED_LOAD_SHIFT would cause issues, since things can assume that nice-0
>> = 1024. However changing SCHED_LOAD_RESOLUTION would be fine, as that is
>> an internal value to the kernel.
>>
>> In addition, changing the non-SLR part of SCHED_LOAD_SHIFT would require
>> recomputing all of prio_to_weight/wmult for the new NICE_0_LOAD.
>
> Not fully looked into the concerns, but the new SCHED_RESOLUTION_SHIFT
> is intended to formalize all the integer metrics that need better resolution.
> It is not special to any metric, so actually it is to de-conflate whoever is
> conflated.

It conflates the userspace-invisible SCHED_LOAD_RESOLUTION with the
userspace-visible value of scale_load_down(NICE_0_LOAD). Increasing
SCHED_LOAD_RESOLUTION must not change scale_load_down(NICE_0_LOAD).
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