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

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Message-ID: <20150910100727.GU3644@twins.programming.kicks-ass.net>
Date:	Thu, 10 Sep 2015 12:07:27 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Yuyang Du <yuyang.du@...el.com>
Cc:	Dietmar Eggemann <dietmar.eggemann@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Steve Muckle <steve.muckle@...aro.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"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 Thu, Sep 10, 2015 at 04:15:20AM +0800, Yuyang Du wrote:
> On Tue, Sep 08, 2015 at 01:50:38PM +0100, Dietmar Eggemann wrote:
> > > It's both a unit and a SCALE/SHIFT problem, SCHED_LOAD_SHIFT and
> > > SCHED_CAPACITY_SHIFT are defined separately so we must be sure to
> > > scale the value in the right range. In the case of cpu_usage which
> > > returns sa->util_avg , it's the capacity range not the load range.
> > 
> > Still don't understand why it's a unit problem. IMHO LOAD/UTIL and
> > CAPACITY have no unit.
> 
> To be more accurate, probably, LOAD can be thought of as having unit,
> but UTIL has no unit.

But I'm thinking that is wrong; it should have one, esp. if we go scale
the thing. Giving it the same fixed point unit as load simplifies the
code.
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