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

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Date:	Wed, 16 Sep 2015 02:39:50 +0800
From:	Yuyang Du <yuyang.du@...el.com>
To:	bsegall@...gle.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@...hat.com" <mingo@...hat.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"mturquette@...libre.com" <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	Juri Lelli <Juri.Lelli@....com>,
	"sgurrappadi@...dia.com" <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by
 capacity_orig

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.

And by the way, with SCHED_RESOLUTION_SHIFT, there will not be SLR anymore, we only
need SCHED_LOAD_SHIFT, which has a low resolution 1*SCHED_RESOLUTION_SHIFT or a high
one 2*SCHED_RESOLUTION_SHIFT. The scale_load*() is the conversion between the 
resolutions of NICE_0 and NICE_0_LOAD.

> 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.
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