Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753289AbZFHHAg (ORCPT ); Mon, 8 Jun 2009 03:00:36 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752248AbZFHHA2 (ORCPT ); Mon, 8 Jun 2009 03:00:28 -0400 Received: from www.tglx.de ([62.245.132.106]:49958 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751799AbZFHHA2 (ORCPT ); Mon, 8 Jun 2009 03:00:28 -0400 Date: Mon, 8 Jun 2009 09:00:14 +0200 (CEST) From: Thomas Gleixner To: Feng Tang cc: "mingo@elte.hu" , "linux-kernel@vger.kernel.org" , "Li, Shaohua" , "Pan, Jacob jun" Subject: Re: [PATCH] tick: add check for the existence of broadcast clock event device In-Reply-To: <20090608144740.62f2ed95@feng-desktop> Message-ID: References: <20090605112711.67e7d5cb@feng-desktop> <20090606204736.00700bd0@feng-desktop> <20090608095730.0c945e78@feng-desktop> <20090608141250.6a5735fa@feng-desktop> <20090608144740.62f2ed95@feng-desktop> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1846 Lines: 37 On Mon, 8 Jun 2009, Feng Tang wrote: > On Mon, 8 Jun 2009 14:33:14 +0800 Thomas Gleixner wrote: > > On Mon, 8 Jun 2009, Feng Tang wrote: > > > Our apbt driver is pretty similar with HPET's, including its cpu > > > hotplug notifier. But our platform only has 2 available apbt to > > > use, otherwise we will configure it just like HPET, using one timer > > > as bc and others for per-cpu ones, then it won't hit this case > > > > > > There are 2 situations, one is for the normal boot, apbt0 will be > > > inited first and registered to OS as cpu0's timer, then tsc/lapic > > > is calculated based on it, and apbt1 is registered later in a > > > fs_initcall() (just like hpet.c does) after basic kernel core is > > > up. so the sequence is: apbt0 --> lapic0 --> lapic1 --> apbt1 > > > > Hmm, I do not like that at all. That explicitely relies on CPU0 doing > > some work which will kick CPU1. That's fragile as hell. > > I understand the concern. apbt0 is inited in a very early boot phase when > the cpu1 is not up yet, and os don't even know wether there is a cpu1, that's > why we registered apbt1 in fs_initcall(). If we explicitly setup apbt1 when > OS brings up cpu1, it is a little brutal and not generic as only our platform > has apbt, and I guess cpu hotplug maintainer won't like it :p Why is that a problem ? You already have a special case for apbt0 in the early setup code. So where is the problem when you have an apbt1 init call on CPU1 _before_ the local APIC is initialized on CPU1. That's definitely saner than relying on magic IPI wakeups. Thanks, tglx -- 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/