linux-kernel - Re: [PATCH v5 5/7] sched: compute runnable load avg in cpu_load and cpu_avg_load_per

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Message-ID: <20130506111041.GA15446@dyad.programming.kicks-ass.net>
Date:	Mon, 6 May 2013 13:10:41 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Paul Turner <pjt@...gle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Alex Shi <alex.shi@...el.com>, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Borislav Petkov <bp@...en8.de>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Morten Rasmussen <morten.rasmussen@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 5/7] sched: compute runnable load avg in cpu_load and
 cpu_avg_load_per_task

On Mon, May 06, 2013 at 03:33:45AM -0700, Paul Turner wrote:
> Yeah, most of the rationale is super hand-wavy; especially the fairly
> arbitrary choice of periods (e.g. busy_idx vs newidle).
> 
> I think the other rationale is:
>   For smaller indicies (e.g. newidle) we speed up response time by
> also cutting motion out of the averages.
> 
> The runnable_avgs themselves actually have a fair bit of history in
> them already (50% is last 32ms); but given that they don't need to be
> cut-off to respond to load being migrated I'm guessing we could
> actually potentially get by with just "instaneous" and "use averages"
> where appropriate?

Sure,. worth a try. If things fall over we can always look at it again.

> We always end up having to re-pick/tune them based on a variety of
> workloads; if we can eliminate them I think it would be a win.

Agreed, esp. the plethora of weird idx things we currently have. If we need to
re-introduce something it would likely only be the busy case and for that we
can immediately link to the balance interval or so.



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