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

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Message-ID: <CAKfTPtDind8HGJwu0odSnNdRpaxp3VB3JWw3eADAp4bL4Ex-Mw@mail.gmail.com>
Date:	Tue, 7 Jan 2014 09:32:04 +0100
From:	Vincent Guittot <vincent.guittot@...aro.org>
To:	Peter Zijlstra <peterz@...radead.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>,
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	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>
Subject: Re: [RFC] sched: CPU topology try

On 6 January 2014 17:31, Peter Zijlstra <peterz@...radead.org> wrote:
> On Mon, Jan 06, 2014 at 02:41:31PM +0100, Vincent Guittot wrote:
>> IMHO, these settings will disappear sooner or later, as an example the
>> idle/busy _idx are going to be removed by Alex's patch.
>
> Well I'm still entirely unconvinced by them..
>
> removing the cpu_load array makes sense, but I'm starting to doubt the
> removal of the _idx things.. I think we want to retain them in some
> form, it simply makes sense to look at longer term averages when looking
> at larger CPU groups.
>
> So maybe we can express the things in log_2(group-span) or so, but we
> need a working replacement for the cpu_load array. Ideally some
> expression involving the blocked load.

Using the blocked load can surely give benefit in the load balance
because it gives a view of potential load on a core but it still decay
with the same speed than runnable load average so it doesn't solve the
issue for longer term average. One way is to have a runnable average
load with longer time window

>
> Its another one of those things I need to ponder more :-)
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