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From: Con Kolivas <kernel@kolivas.org>
To: malc <av1474@comtv.ru>
Cc: linux-kernel@vger.kernel.org
Subject: Re: CPU load
Date: Mon, 12 Feb 2007 17:12:50 +1100	[thread overview]
Message-ID: <200702121712.50168.kernel@kolivas.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0702120849310.903@home.oyster.ru>

On Monday 12 February 2007 16:54, malc wrote:
> On Mon, 12 Feb 2007, Con Kolivas wrote:
> > On 12/02/07, Vassili Karpov <av1474@comtv.ru> wrote:
>
> [..snip..]
>
> > 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.
>
> Thank you very much. This somewhat contradicts what i saw (and outlined
> in usnet article), namely the mplayer+/dev/rtc case. Unless ofcourse
> /dev/rtc interrupt is considered to be the same as the interrupt from
> PIT (on X86 that is)
>
> P.S. Perhaps it worth documenting this in the documentation? I caused
>       me, and perhaps quite a few other people, a great deal of pain and
>       frustration.

Lots of confusion comes from this, and often people think their pc suddenly 
uses a lot less cpu when they change from 1000HZ to 100HZ and use this as an 
argument/reason for changing to 100HZ when in fact the massive _reported_ 
difference is simply worse accounting. Of course there is more overhead going 
from 100 to 1000 but it doesn't suddenly make your apps use 10 times more 
cpu.

-- 
-ck

  reply	other threads:[~2007-02-12  6:13 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 [this message]
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
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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