Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757781Ab2BMTy2 (ORCPT ); Mon, 13 Feb 2012 14:54:28 -0500 Received: from mail-gy0-f174.google.com ([209.85.160.174]:57191 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757766Ab2BMTy0 (ORCPT ); Mon, 13 Feb 2012 14:54:26 -0500 MIME-Version: 1.0 In-Reply-To: <87d39xj955.fsf@rustcorp.com.au> References: <1328055439-9441-1-git-send-email-venki@google.com> <20120201140125.c656df41.akpm@linux-foundation.org> <87d39xj955.fsf@rustcorp.com.au> Date: Mon, 13 Feb 2012 11:54:26 -0800 Message-ID: Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 From: Tony Luck To: Rusty Russell Cc: Andrew Morton , Venkatesh Pallipadi , KOSAKI Motohiro , KOSAKI Motohiro , Mike Travis , "Srivatsa S. Bhat" , "Paul E. McKenney" , "Rafael J. Wysocki" , Paul Gortmaker , linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1270 Lines: 33 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!) -Tony -- 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/