Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933024AbXBLGN2 (ORCPT ); Mon, 12 Feb 2007 01:13:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933025AbXBLGN2 (ORCPT ); Mon, 12 Feb 2007 01:13:28 -0500 Received: from mail07.syd.optusnet.com.au ([211.29.132.188]:41887 "EHLO mail07.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933024AbXBLGN1 (ORCPT ); Mon, 12 Feb 2007 01:13:27 -0500 From: Con Kolivas To: malc Subject: Re: CPU load Date: Mon, 12 Feb 2007 17:12:50 +1100 User-Agent: KMail/1.9.5 Cc: linux-kernel@vger.kernel.org References: <8cd998d50702112144y38958d27saec4196f6f5d5236@mail.gmail.com> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200702121712.50168.kernel@kolivas.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1627 Lines: 36 On Monday 12 February 2007 16:54, malc wrote: > On Mon, 12 Feb 2007, Con Kolivas wrote: > > On 12/02/07, Vassili Karpov 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 - 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/