From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 20 Dec 2001 17:34:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 20 Dec 2001 17:34:09 -0500 Received: from gateway-1237.mvista.com ([12.44.186.158]:1786 "EHLO hermes.mvista.com") by vger.kernel.org with ESMTP id ; Thu, 20 Dec 2001 17:33:50 -0500 Message-ID: <3C226708.FECAE3CD@mvista.com> Date: Thu, 20 Dec 2001 14:32:40 -0800 From: george anzinger Organization: Monta Vista Software X-Mailer: Mozilla 4.77 [en] (X11; U; Linux 2.2.12-20b i686) X-Accept-Language: en MIME-Version: 1.0 To: "Martin A. Brooks" CC: Mark Hahn , LKML Subject: Re: asymmetric multiprocessing In-Reply-To: <1008858802.431.43.camel@unhygienix> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org "Martin A. Brooks" wrote: > > On Thu, 2001-12-20 at 14:13, Mark Hahn wrote: > > not supported (and frowned upon by the spec). the issue is TSC, > > of course, and it's definitely not clear whether the normal case > > (correctly configured SMP) should be burdoned by support for > > mixed-clock chips. > > I'm no expert on MP, hence I fail to see why differing clock speeds > between CPUs should be a problem providing the system bus rates are > constant. As each CPU would be rated differently as far as bogomips are > concerned, couldn't the scheduler apply load accordingly? > But then you are forcing the system to include cpu information each time it reads the TSC. For example, the TSC is currently used to provide the sub jiffie resolution for the system clock. If you also need to include which cpu you run into a couple of problems: a) what if the start TSC is read from a different cpu than the end TSC? (In this case the start is the last jiffie interrupt and the end is "now" when the time is being requested.) b.) The conversion to micro seconds depends on the clock rate, i.e. the TSC clock rate. -- George george@mvista.com High-res-timers: http://sourceforge.net/projects/high-res-timers/ Real time sched: http://sourceforge.net/projects/rtsched/