linux-kernel - Re: Meaningless load?

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Date:	Thu, 11 Oct 2012 09:19:49 +0200
From:	Simon Klinkert <simon.klinkert@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>
Cc:	LKML <linux-kernel@...r.kernel.org>, mingo@...hat.com,
	Trond.Myklebust@...app.com
Subject: Re: Meaningless load?


On 10.10.2012, at 18:22, Peter Zijlstra  wrote:

> On Wed, 2012-10-10 at 17:44 +0200, Simon Klinkert wrote:
>> I'm just wondering if the 'load' is really meaningful in this
>> scenario. The machine is the whole time fully responsive and looks
>> fine to me but maybe I didn't understand correctly what the load
>> should mean. Is there any sensible interpretation of the load?
> 
> I'll leave meaningful aside, but uninterruptible (D state) is part of
> how the load thing is defined, so your 500 result is correct.

Yes, the calculation of the load is correct but I still don't know how I should interpret the load…

On 11.10.2012, at 06:02, Mike Galbraith wrote:

> Makes perfect sense to me.  Work _is_ stack this high.  We don't and
> can't know whether the mountain is made of popcorn balls or boulders.

That's the point. Afaik the D state never represents 'work'. These processes are waiting for something.

Let's say we have 10,000 processes in the D state (and thus a load of ~10,000) doing nothing. What should the load tell me? The machine is under fire? There is nothing to do? There might be something to do but the machine doesn't know?

Simon


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