From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752694Ab2DBOid (ORCPT ); Mon, 2 Apr 2012 10:38:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45106 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751291Ab2DBOic (ORCPT ); Mon, 2 Apr 2012 10:38:32 -0400 From: Jeff Moyer To: "Srivatsa S. Bhat" Cc: Sasha Levin , Nick Bowler , linux-kernel@vger.kernel.org, Kay Sievers Subject: Re: the maxcpus= boot parameter broke somewhere along the line References: <20120306164835.GA26094@elliptictech.com> <4F578198.8060708@linux.vnet.ibm.com> <4F59E802.6070301@linux.vnet.ibm.com> <4F79B891.8020704@linux.vnet.ibm.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Mon, 02 Apr 2012 10:38:27 -0400 In-Reply-To: <4F79B891.8020704@linux.vnet.ibm.com> (Srivatsa S. Bhat's message of "Mon, 02 Apr 2012 20:02:49 +0530") Message-ID: User-Agent: Gnus/5.110011 (No Gnus v0.11) Emacs/23.1 (gnu/linux) 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 "Srivatsa S. Bhat" writes: > On 04/02/2012 07:35 PM, Jeff Moyer wrote: > >> "Srivatsa S. Bhat" writes: >> >>> Looking at the mention of udev above, and considering the commit you bisected >>> to, I think it would be good to see whether someone is writing 1 to >>> /sys/device/system/cpu/cpu*/online and hence the cpus are getting hot-added >>> towards the end of boot. Maybe that sounds stupid, but worth a try :) >>> >>> So can you try the debug patch below? It applies on latest linux-3.3-rc6+ >> >> Sorry it took me so long to get back to you. You're patch did, in fact, >> trigger: >> >> udev: starting version 147 >> CPU 3 online initated from userspace >> SMP alternatives: switching to SMP code >> WARNING! power/level is deprecated; use power/control instead >> Booting Node 0 Processor 3 APIC 0x3 >> NMI watchdog: enabled, takes one hw-pmu counter. >> CPU 1 online initated from userspace >> Booting Node 0 Processor 1 APIC 0x2 >> NMI watchdog: enabled, takes one hw-pmu counter. >> CPU 2 online initated from userspace >> Booting Node 0 Processor 2 APIC 0x1 >> NMI watchdog: enabled, takes one hw-pmu counter. >> CPU 1 online initated from userspace >> CPU 3 online initated from userspace >> CPU 2 online initated from userspace >> > > > Aha! Just like I thought! > So there is no kernel bug with respect to the maxcpus= boot parameter :-) But this IS a change in behaviour (using older kernels, the maxcpus= boot parameter works just fine). So, what exactly has changed is my question, and what is the right way to fix it? Cheers, Jeff