From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758406Ab2BJPwS (ORCPT ); Fri, 10 Feb 2012 10:52:18 -0500 Received: from casper.infradead.org ([85.118.1.10]:60081 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758124Ab2BJPwR (ORCPT ); Fri, 10 Feb 2012 10:52:17 -0500 Subject: Re: [PATCH 0/4] CPU hotplug, cpusets: Fix CPU online handling related to cpusets From: Peter Zijlstra To: Ingo Molnar Cc: "Srivatsa S. Bhat" , paul@paulmenage.org, rjw@sisk.pl, tj@kernel.org, frank.rowand@am.sony.com, pjt@google.com, tglx@linutronix.de, lizf@cn.fujitsu.com, prashanth@linux.vnet.ibm.com, paulmck@linux.vnet.ibm.com, vatsa@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "akpm@linux-foundation.org" In-Reply-To: <20120209151158.GA22489@elte.hu> References: <20120207185411.7482.43576.stgit@srivatsabhat.in.ibm.com> <1328671335.2482.72.camel@laptop> <4F32174E.2050207@linux.vnet.ibm.com> <20120209075701.GE18387@elte.hu> <4F3386E9.7090606@linux.vnet.ibm.com> <20120209151158.GA22489@elte.hu> Content-Type: text/plain; charset="UTF-8" Date: Fri, 10 Feb 2012 16:52:07 +0100 Message-ID: <1328889127.25989.14.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.32.2 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-02-09 at 16:11 +0100, Ingo Molnar wrote: > > My understanding of the code is that when a CPU is taken > > offline, it is removed from all the cpusets and then the > > scan_for_empty_cpusets() function is run to move tasks from > > empty cpusets to their parent cpusets. > > Why is that done that way? offlining a CPU should be an > invariant as far as cpusets are concerned. Can't, tasks need to run someplace. There's two choices, add a still online cpu to the now empty cpuset or move the tasks to a parent that still has online cpus. Both are destructive.