Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757189Ab2JIX1I (ORCPT ); Tue, 9 Oct 2012 19:27:08 -0400 Received: from mail-pa0-f46.google.com ([209.85.220.46]:36573 "EHLO mail-pa0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756946Ab2JIX1D (ORCPT ); Tue, 9 Oct 2012 19:27:03 -0400 Date: Tue, 9 Oct 2012 16:27:01 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Peter Zijlstra cc: Tang Chen , mingo@redhat.com, miaox@cn.fujitsu.com, wency@cn.fujitsu.com, linux-kernel@vger.kernel.org, linux-numa@vger.kernel.org Subject: Re: [PATCH] Do not use cpu_to_node() to find an offlined cpu's node. In-Reply-To: <1349815676.7880.85.camel@twins> Message-ID: References: <1349665183-11718-1-git-send-email-tangchen@cn.fujitsu.com> <1349780256.7880.12.camel@twins> <1349815676.7880.85.camel@twins> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) 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 Content-Length: 1711 Lines: 37 On Tue, 9 Oct 2012, Peter Zijlstra wrote: > Well the code they were patching is in the wakeup path. As I think Tang > said, we leave !runnable tasks on whatever cpu they ran on last, even if > that cpu is offlined, we try and fix up state when we get a wakeup. > > On wakeup, it tries to find a cpu to run on and will try a cpu of the > same node first. > > Now if that node's entirely gone away, it appears the cpu_to_node() map > will not return a valid node number. > > I think that's a change in behaviour, it didn't used to do that afaik. > Certainly this code hasn't change in a while. > If cpu_to_node() always returns a valid node id even if all cpus on the node are offline, then the cpumask_of_node() implementation, which the sched code is using, should either return an empty cpumask (if node_to_cpumask_map[nid] isn't freed) or cpu_online_mask. The change in behavior here occurred because cpu_hotplug-unmap-cpu2node-when-the-cpu-is-hotremoved.patch in -mm doesn't return a valid node id and forces it to return -1 so a kzalloc_node(..., -1) fallsback to allocate anywhere. But if you only need cpu_to_node() when waking up to find a runnable cpu for this NUMA information, then I think you can just change the kzalloc_node() in alloc_{fair,rt}_sched_group() to do kzalloc(..., cpu_online(cpu) ? cpu_to_node(cpu) : NUMA_NO_NODE). [ The changelog here is confusing because it's fixing a problem in linux-next without saying so. ] -- 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/