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From: malc <av1474@comtv.ru>
To: Pavel Machek <pavel@ucw.cz>
Cc: Con Kolivas <kernel@kolivas.org>, linux-kernel@vger.kernel.org
Subject: Re: CPU load
Date: Wed, 14 Feb 2007 01:01:26 +0300 (MSK)	[thread overview]
Message-ID: <Pine.LNX.4.64.0702140059390.727@home.oyster.ru> (raw)
In-Reply-To: <20070212143219.GB5226@ucw.cz>

On Mon, 12 Feb 2007, Pavel Machek wrote:

> 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.

Slightly changed version of hog(around 3 lines in total changed) does that
easily on 2.6.18.3 on PPC.

http://www.boblycat.org/~malc/apc/load-hog-ppc.png

-- 
vale

  reply	other threads:[~2007-02-13 22:00 UTC|newest]

Thread overview: 28+ 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
2007-02-13 22:01     ` malc [this message]
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 --
2018-03-27 11:44 CPU Load Ryan Meulenkamp
2018-03-29  1:24 ` Andre McCurdy
2018-03-29  6:42   ` Jussi Laako
2007-02-12 16:57 CPU load 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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