From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757646AbZAGOVH (ORCPT ); Wed, 7 Jan 2009 09:21:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753944AbZAGOUz (ORCPT ); Wed, 7 Jan 2009 09:20:55 -0500 Received: from casper.infradead.org ([85.118.1.10]:60207 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751627AbZAGOUy (ORCPT ); Wed, 7 Jan 2009 09:20:54 -0500 Subject: Re: SMP timer issue From: Peter Zijlstra To: melwyn lobo Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar In-Reply-To: <121039230901062108s7312343cwaf81feebfcf8d734@mail.gmail.com> References: <121039230901062108s7312343cwaf81feebfcf8d734@mail.gmail.com> Content-Type: text/plain Content-Transfer-Encoding: 7bit Date: Wed, 07 Jan 2009 15:20:51 +0100 Message-Id: <1231338051.11687.293.camel@twins> Mime-Version: 1.0 X-Mailer: Evolution 2.24.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-01-07 at 10:38 +0530, melwyn lobo wrote: > Hello All, > Following reply from Russell on the ARM mailing list, I have posted my > question on this list. > > We have ported the arm kernel 2.6.24 to ARM Cortex dual core > processor. My question is regarding timer optimization. > At present we have three timers for the two cores as follows; > 1. MTU which provides the system tick and in the absence of local > timers provides IPI_TIMER messages to other processors. > 2. Localtimer for CPU0 > 3. Localtimer for CPU1 > > So presently (when local timers are enabled) there are 3 interrupts > for every tick. I want to optimize the logic performed by MTU into the > local timer of CPU0 so that this one serves as the system tick. Thus > there would be no need for MTU interrupts and it would serve only as a > clock source. > > My question in particular: > 1. Is there some platform which has already done this ? > 2. Is this possible without modifying existing kernel framework? > 3. How to update jiffies during boot when localtimer has not yet been setup? > > Eagerly awaiting for some advice/comments. There is plenty code in the hrtimer stuff to make the cpu local timers (which I presume are used to implement hrtimer clockevents) do the jiffie tick. I've no idea how to hook all that up, but added some folks who might know to the CC.