Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753658AbZCKJue (ORCPT ); Wed, 11 Mar 2009 05:50:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751947AbZCKJuZ (ORCPT ); Wed, 11 Mar 2009 05:50:25 -0400 Received: from mail-gx0-f167.google.com ([209.85.217.167]:44523 "EHLO mail-gx0-f167.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbZCKJuY convert rfc822-to-8bit (ORCPT ); Wed, 11 Mar 2009 05:50:24 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=YJtcfzGgJlCkEh0MGmmRsjFs0DYtaxhiXdRGyMo1Wryx7yRy6vlBJHN0/p+QtfXnlZ /ALIMapiOZgGYglcYJSNTZVh7cSPwnIUuFBsfw0LYh7L8g6q9wcg18aUlhGi8a0ygrYd lt3HgvR4XQ756egvV0L/rSG4h98mgakNyX074= MIME-Version: 1.0 In-Reply-To: <20090310094810.2ffe1f63.akpm@linux-foundation.org> References: <1236321780-28718-1-git-send-email-cooloney@kernel.org> <1236321780-28718-3-git-send-email-cooloney@kernel.org> <20090306143756.738db0ee.akpm@linux-foundation.org> <1236679631.5183.72.camel@dy> <8bd0f97a0903100325k6cbcf73ek8e5f3723b2c4bb0a@mail.gmail.com> <20090310094810.2ffe1f63.akpm@linux-foundation.org> Date: Wed, 11 Mar 2009 17:50:21 +0800 Message-ID: <7d86d44a0903110250l9bcccd7led5558068f153522@mail.gmail.com> Subject: Re: [PATCH 02/18] Blackfin Serial Driver: use barrier instead of cpu_relax for Blackfin SMP like patch From: graff yang To: Andrew Morton Cc: Mike Frysinger , gyang , Bryan Wu , alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2257 Lines: 60 On Wed, Mar 11, 2009 at 12:48 AM, Andrew Morton wrote: > > On Tue, 10 Mar 2009 06:25:08 -0400 Mike Frysinger wrote: > > > On Tue, Mar 10, 2009 at 06:07, gyang wrote: > > > On Fri, 2009-03-06 at 14:37 -0800, Andrew Morton wrote: > > >> On Fri,  6 Mar 2009 14:42:44 +0800 > > >> Bryan Wu wrote: > > >> > > >> > From: Graf Yang > > >> > > > >> > We are making a SMP like patch to blackfin, cpu_relax() is replaced by a > > >> > data cache flush function which will count it to a per-cpu counter. > > >> > If this serial function is called too early, the per-cpu data area have > > >> > not been initialized, this call will cause crash. > > >> > > >> That's a bug in blackfin architecture support.  The kernel should be > > >> able to call cpu_relax() at any time, surely.  It's a very low-level > > >> and simple thing. > > >> > > >> > So we'd like to use barrier() instead of cpu_relax(). > > >> > > > >> > > >> barrier() is purely a compiler concept.  We might as well just remove > > >> the cpu_relax() altogether. > > > > > > Do you mean remove cpu_relax(), and either not add barrier() here? > > > > afaik, early printk all runs before SMP is setup, so having it be a > > 100% busy wait is fine > > No, blackfin is busted, please fix this bug in blackfin core. > > What happens if core kernel code decides to run cpu_relax() prior to > initialising per-cpu data? cpu_relax() will call smp_mb(), and it need to invalidate data-cache in blackfin smp-like kernel, the cache flush number is increased and recorded into a per-cpu data. When cpu_relax() is called from early-printk functions, the per-cpu data areas have not been initialized. > -- > 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/ -- -Graff -- 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/