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

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Date:	Wed, 16 Sep 2015 10:06:24 -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 Tue, Sep 15, 2015 at 10:11:41AM -0700, bsegall@...gle.com wrote:
>> >
>> > I guess you are saying we are conflating NICE_0 with NICE_0_LOAD. But to me,
>> > they are just integer metrics, needing a resolution respectively. That is it.
>> 
>> Yes this would change nothing at the moment post-expansion, that's not
>> the point. SLR being 10 bits and the nice-0 being 1024 are completely
>> and utterly unrelated and the headers should not pretend they need to be
>> the same value,
>
> I never said they are related, why should they be related. And they need or
> need not to be the same value, fine.
>
> However, the SLR has to be a value. It is because it mighe be 10 or 20 (LOAD),
> therefore I make SCHED_RESOLUTION_SHIFT 10 (kind of a denominator). Not the
> other way around.
>
> We can define SCHED_RESOLUTION_SHIFT 1, and then define SLR = x * SCHED_RESOLUTION_SHIFT
> with x being a random number, if you must.

That's sorta the point - you could do this and it would be just as (non-)sensical.

>
>> any more than there should be a #define that is shared
>> with every other use of 1024 in the kernel.
>
> The point really is, metrics (if not many ) need resolution, not just NICE_0_LOAD does. 
> You can choose to either hardcode a number, like SCHED_CAPACITY_SHIFT now,
> or you can use SCHED_RESOLUTION_SHIFT, which is even as simple as a sign to say what
> the defined is (the scaled one with a better resolution vs. the original one).
> I guess this is to say we now have a (no-big-deal) resolution system.

Yes they were chosen for similar reasons, but they are not conceptually
related, and you couldn't decide to just bump up all the resolutions by
changing SCHED_RESOLUTION_SHIFT, so doing this would just be misleading.
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