Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932279Ab2BMUnE (ORCPT ); Mon, 13 Feb 2012 15:43:04 -0500 Received: from mail-yw0-f46.google.com ([209.85.213.46]:33644 "EHLO mail-yw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932201Ab2BMUnB convert rfc822-to-8bit (ORCPT ); Mon, 13 Feb 2012 15:43:01 -0500 MIME-Version: 1.0 In-Reply-To: <4F3971A1.5010305@linux.vnet.ibm.com> References: <1328055439-9441-1-git-send-email-venki@google.com> <20120201140125.c656df41.akpm@linux-foundation.org> <87d39xj955.fsf@rustcorp.com.au> <4F3971A1.5010305@linux.vnet.ibm.com> Date: Mon, 13 Feb 2012 12:43:00 -0800 Message-ID: Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 From: Venki Pallipadi To: "Srivatsa S. Bhat" Cc: Tony Luck , Rusty Russell , Andrew Morton , KOSAKI Motohiro , KOSAKI Motohiro , Mike Travis , "Paul E. McKenney" , "Rafael J. Wysocki" , Paul Gortmaker , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1938 Lines: 47 On Mon, Feb 13, 2012 at 12:25 PM, Srivatsa S. Bhat wrote: > On 02/14/2012 01:24 AM, Tony Luck wrote: > >> On Thu, Feb 2, 2012 at 12:03 PM, Rusty Russell wrote: >>> IIRC playing with 3 archs boot code seemed like a recipe for disaster. >>> Feel free to try to fix this in -next though, and see what breaks... >> >> ia64 is what breaks ... well not actually broken ... but some very >> weird delays that >> show up in different places depending on whether this patch is present. >> >> First linux-next kernel to be blessed with this patch was >> next-20120210. Booting it >> I see: >> [ ? ?7.164233] Switching to clocksource itc >> [ ?146.077315] pnp: PnP ACPI init >> >> An ugly 138.913 second delay. ?Digging in the code showed that the bad bits >> happened inside stop_machine() >> >> Reverting just this patch makes this big delay disappear: >> >> [ ? 32.780232] Switching to clocksource itc >> [ ? 32.832100] pnp: PnP ACPI init >> >> but notice that it takes 25 extra seconds to get to this point in the >> boot (and while >> we expect to save some time by not re-computing num_online_cpus each time we >> need it ... this looks to be a lot more than I'd expect!) >> > > > Oh no!! ia64 directly uses cpu_set() and cpu_clear() on cpu_online_map!! > Grr.. It means num_online_cpus can be different from the actual number of > online cpus because it doesn't go through the set_cpu_online() path.. I haven't > yet pin-pointed the exact problem, but this definitely doesn't look good... > This feels like a minefield in general. ia64, mips and um seems to have cpu_set and cpu_clear of cpu_online_map and/or cpu_possible_map in there. -- 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/