Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751295Ab0KLGTJ (ORCPT ); Fri, 12 Nov 2010 01:19:09 -0500 Received: from cantor2.suse.de ([195.135.220.15]:40057 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750907Ab0KLGTH convert rfc822-to-8bit (ORCPT ); Fri, 12 Nov 2010 01:19:07 -0500 From: Nikanth Karthikesan Organization: suse.de To: Myron Stowe Subject: Re: divide error in select_task_rq_fair() Date: Fri, 12 Nov 2010 11:52:29 +0530 User-Agent: KMail/1.12.4 (Linux/2.6.31.12-0.2-default; KDE/4.3.5; x86_64; ; ) Cc: Eric Dumazet , Bjorn Helgaas , Ingo Molnar , Peter Zijlstra , Venkatesh Pallipadi , Nikhil Rao , Takuya Yoshikawa , linux-kernel@vger.kernel.org, rjenties@google.com References: <20101104041236.GA9389@helgaas.com> <1288937844.3234.1.camel@edumazet-laptop> <1289500084.2698.12.camel@zim> In-Reply-To: <1289500084.2698.12.camel@zim> MIME-Version: 1.0 Content-Type: Text/Plain; charset="utf-8" Content-Transfer-Encoding: 8BIT Message-Id: <201011121152.30204.knikanth@suse.de> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3769 Lines: 94 On Thursday 11 November 2010 23:58:04 Myron Stowe wrote: > On Fri, 2010-11-05 at 07:17 +0100, Eric Dumazet wrote: > > Le jeudi 04 novembre 2010 à 20:00 -0600, Bjorn Helgaas a écrit : > > > Is that going to help you debug the problem? The solution is not going > > > to be something like "set NR_CPUS=x". If NR_CPUS is too small, the > > > machine should still *boot*, even if we can't use all the CPUs in the > > > box. > > > > Yes, it will help to understand the layout of cpu / domains and make > > appropriate changes. > > > > Alternative is you send me such a machine :=) > > I opened a BZ on this issue as it seems to be a regression - > https://bugzilla.kernel.org/show_bug.cgi?id=22662 > > I also, as indicated in the BZ, bisected the kernel which gave the > following results and reverting 50f2d7f682f9c0ed58191d0982fe77888d59d162 > did re-enable booting on the box in question (an HP dl980g7). Let me > know what further info you need or patches to test for debugging this. > > Thanks, > > commit 50f2d7f682f9c0ed58191d0982fe77888d59d162 > Author: Nikanth Karthikesan > Date: Thu Sep 30 17:34:10 2010 +0530 > > x86, numa: Assign CPUs to nodes in round-robin manner on fake NUMA > > commit d9c2d5ac6af87b4491bff107113aaf16f6c2b2d9 "x86, numa: Use > near(er) online node instead of roundrobin for NUMA" changed NUMA > initialization on Intel to choose the nearest online node or first node. > Fake NUMA would be better of with round-robin initialization, instead of > the all CPUS on first node. Change the choice of first node, back to > round-robin. > > For testing NUMA kernel behaviour without cpusets and NUMA aware > applications, it would be better to have cpus in different nodes, > rather than all in a single node. With cpusets migration of tasks > scenarios cannot not be tested. > > I guess having it round-robin shouldn't affect the use cases for all > cpus on the first node. > > The code comments in arch/x86/mm/numa_64.c:759 indicate that this used > to be the case, which was changed by commit d9c2d5ac6. It changed from > roundrobin to nearer or first node. And I couldn't find any reason for > this change in its changelog. > > Signed-off-by: Nikanth Karthikesan > Cc: David Rientjes > Signed-off-by: Andrew Morton > > > Thanks > Can you try with this patch? Thanks Nikanth Fallback to first node, if the node is not online. Fixes regression of commit 50f2d7f682f9c0ed58191d0982fe77888d59d162 x86, numa: Assign CPUs to nodes in round-robin manner on fake NUMA When some of the NUMA nodes are disabled, and the CPUs are assigned in round-robin fashion, CPUs might be assigned to disabled nodes resulting in the crash. While using round-robin assignment, check if the node is online. If the node is not online, use the first online node. Reported-by: Bjorn Helgaas Signed-off-by: Nikanth Karthikesan --- diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index d16c2c5..f31237c 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -287,6 +287,8 @@ static void __cpuinit srat_detect_node(struct cpuinfo_x86 *c) if (node == NUMA_NO_NODE || !node_online(node)) { /* reuse the value from init_cpu_to_node() */ node = cpu_to_node(cpu); + if (!node_online(node)) + node = first_node(node_online_map); } numa_set_node(cpu, node); #endif -- 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/