linux-kernel - Re: [RFC] sched: CPU topology try

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Message-ID: <20140107141059.GY3694@twins.programming.kicks-ass.net>
Date:	Tue, 7 Jan 2014 15:10:59 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Dietmar Eggemann <dietmar.eggemann@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"pjt@...gle.com" <pjt@...gle.com>,
	Morten Rasmussen <Morten.Rasmussen@....com>,
	"cmetcalf@...era.com" <cmetcalf@...era.com>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"alex.shi@...aro.org" <alex.shi@...aro.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>,
	"paulmck@...ux.vnet.ibm.com" <paulmck@...ux.vnet.ibm.com>,
	"corbet@....net" <corbet@....net>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"len.brown@...el.com" <len.brown@...el.com>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
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	"james.hogan@...tec.com" <james.hogan@...tec.com>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>
Subject: Re: [RFC] sched: CPU topology try

On Tue, Jan 07, 2014 at 02:22:20PM +0100, Peter Zijlstra wrote:

I just realized there's two different p's in there.

> Ah, another way of looking at it is that the avg without blocked
> component is a 'now' picture. It is the load we are concerned with right
> now.
> 
> The more blocked we add the further out we look; with the obvious limit
> of the entire averaging period.
> 
> So the avg that is runnable is right now, t_0; the avg that is runnable +
> blocked is t_0 + p, where p is the avg period over which we expect the
> blocked contribution to appear.

So the above p for period, is unrelated to the below p which is a
probability function.

> So something like:
> 
>   avg = runnable + p(i) * blocked; where p(i) \e [0,1]
> 
> could maybe be used to replace the cpu_load array and still represent
> the concept of looking at a bigger picture for larger sets. Leaving open
> the details of the map p.

We probably want to assume task wakeup is constant over time, so p (our
probability function) should probably be an exponential distribution.
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