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From: Pavel Machek <pavel@ucw.cz>
To: Con Kolivas <kernel@kolivas.org>
Cc: Vassili Karpov <av1474@comtv.ru>, linux-kernel@vger.kernel.org
Subject: Re: CPU load
Date: Mon, 12 Feb 2007 14:32:20 +0000	[thread overview]
Message-ID: <20070212143219.GB5226@ucw.cz> (raw)
In-Reply-To: <8cd998d50702112144y38958d27saec4196f6f5d5236@mail.gmail.com>

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

  parent reply	other threads:[~2007-02-13 18:28 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-02-12  5:33 Vassili Karpov
2007-02-12  5:44 ` Con Kolivas
2007-02-12  5:54   ` malc
2007-02-12  6:12     ` Con Kolivas
2007-02-12  7:10       ` malc
2007-02-12  7:29         ` Con Kolivas
2007-02-12  5:55   ` Stephen Rothwell
2007-02-12  6:08     ` Con Kolivas
2007-02-12 14:32   ` Pavel Machek [this message]
2007-02-13 22:01     ` malc
2007-02-13 22:08       ` Con Kolivas
2007-02-14  7:28         ` malc
2007-02-14  8:09           ` Con Kolivas
2007-02-14 20:45           ` Pavel Machek
2007-02-25 10:35             ` malc
2007-02-26  9:28               ` Pavel Machek
2007-02-26 10:42                 ` malc
2007-02-26 16:38                   ` Randy Dunlap
2007-02-12 18:05   ` malc
  -- strict thread matches above, loose matches on Subject: below --
2007-02-12 16:57 Andrew Burgess
2007-02-12 18:15 ` malc
2002-07-10 14:50 David Chow
2002-07-10 16:54 ` William Lee Irwin III
2002-07-10 17:49   ` Robert Love
2002-07-26 17:38     ` David Chow

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