Date: Mon, 12 Feb 2007 08:54:25 +0300 (MSK)
From: malc <av1474@comtv.ru>
To: Con Kolivas <kernel@kolivas.org>
cc: linux-kernel@vger.kernel.org
Subject: Re: CPU load
In-Reply-To: <8cd998d50702112144y38958d27saec4196f6f5d5236@mail.gmail.com>
Message-ID: <Pine.LNX.4.64.0702120849310.903@home.oyster.ru>
References: <loom.20070212T063225-663@post.gmane.org>
 <8cd998d50702112144y38958d27saec4196f6f5d5236@mail.gmail.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1157
Lines: 29

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.

-- 
vale
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/