linux-kernel - Re: CPU load

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Message-ID: <20070212143219.GB5226@ucw.cz>
Date:	Mon, 12 Feb 2007 14:32:20 +0000
From:	Pavel Machek <pavel@....cz>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	Vassili Karpov <av1474@...tv.ru>, linux-kernel@...r.kernel.org
Subject: Re: CPU load

Hi!

> The kernel looks at what is using cpu _only_ during the 
> timer
> interrupt. Which means if your HZ is 1000 it looks at 
> what is running
> at precisely the moment those 1000 timer ticks occur. It 
> is
> theoretically possible using this measurement system to 
> use >99% cpu
> and record 0 usage if you time your cpu usage properly. 
> It gets even
> more inaccurate at lower HZ values for the same reason.

I have (had?) code that 'exploits' this. I believe I could eat 90% of cpu
without being noticed.
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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