Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758126Ab2BMUzs (ORCPT ); Mon, 13 Feb 2012 15:55:48 -0500 Received: from e28smtp09.in.ibm.com ([122.248.162.9]:51434 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754173Ab2BMUzr (ORCPT ); Mon, 13 Feb 2012 15:55:47 -0500 Message-ID: <4F3978C5.7080901@linux.vnet.ibm.com> Date: Tue, 14 Feb 2012 02:25:33 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux i686; rv:9.0) Gecko/20111222 Thunderbird/9.0 MIME-Version: 1.0 To: Venki Pallipadi 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 Subject: Re: [PATCH] Avoid mask based num_possible_cpus and num_online_cpus -v5 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> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit x-cbid: 12021320-2674-0000-0000-00000353D5AB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2288 Lines: 59 On 02/14/2012 02:13 AM, Venki Pallipadi wrote: > 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. > Since I had almost never seen code using "cpu_online_map" instead of "cpu_online_mask", I hadn't checked it while reviewing your patch... :-( Honestly, it is only now that I realized that there is this other variant too! Regards, Srivatsa S. Bhat -- 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/