Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig

From: bsegall@google.com
To: Yuyang Du <yuyang.du@intel.com>
Cc: Morten Rasmussen <morten.rasmussen@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Steve Muckle <steve.muckle@linaro.org>,
	"mingo\@redhat.com" <mingo@redhat.com>,
	"daniel.lezcano\@linaro.org" <daniel.lezcano@linaro.org>,
	"mturquette\@baylibre.com" <mturquette@baylibre.com>,
	"rjw\@rjwysocki.net" <rjw@rjwysocki.net>,
	Juri Lelli <Juri.Lelli@arm.com>,
	"sgurrappadi\@nvidia.com" <sgurrappadi@nvidia.com>,
	"pang.xunlei\@zte.com.cn" <pang.xunlei@zte.com.cn>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/6] sched/fair: Get rid of scaling utilization by capacity_orig
Date: Wed, 16 Sep 2015 10:06:24 -0700	[thread overview]
Message-ID: <xm26mvwm9tv3.fsf@sword-of-the-dawn.mtv.corp.google.com> (raw)
In-Reply-To: <20150915183950.GA28071@intel.com> (Yuyang Du's message of "Wed, 16 Sep 2015 02:39:50 +0800")

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

> On Tue, Sep 15, 2015 at 10:11:41AM -0700, bsegall@google.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.