From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934051Ab3BMOoT (ORCPT ); Wed, 13 Feb 2013 09:44:19 -0500 Received: from mga11.intel.com ([192.55.52.93]:22065 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756032Ab3BMOoS (ORCPT ); Wed, 13 Feb 2013 09:44:18 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,657,1355126400"; d="scan'208";a="290605921" Message-ID: <511BA6BC.3060707@intel.com> Date: Wed, 13 Feb 2013 22:44:12 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120912 Thunderbird/15.0.1 MIME-Version: 1.0 To: Peter Zijlstra CC: torvalds@linux-foundation.org, mingo@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, arjan@linux.intel.com, bp@alien8.de, pjt@google.com, namhyung@kernel.org, efault@gmx.de, vincent.guittot@linaro.org, gregkh@linuxfoundation.org, preeti@linux.vnet.ibm.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org Subject: Re: [patch v4 02/18] sched: select_task_rq_fair clean up References: <1358996820-23036-1-git-send-email-alex.shi@intel.com> <1358996820-23036-3-git-send-email-alex.shi@intel.com> <1360664089.4485.6.camel@laptop> In-Reply-To: <1360664089.4485.6.camel@laptop> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/12/2013 06:14 PM, Peter Zijlstra wrote: > On Thu, 2013-01-24 at 11:06 +0800, Alex Shi wrote: >> It is impossible to miss a task allowed cpu in a eligible group. > > I suppose your reasoning goes like: tsk->cpus_allowed is protected by > ->pi_lock, we hold this, therefore it cannot change and > find_idlest_group() dtrt? yes. > > We can then state that this is due to adding proper serialization to > tsk->cpus_allowed. > >> And since find_idlest_group only return a different group which >> excludes old cpu, it's also impossible to find a new cpu same as old >> cpu. > > Sounds plausible, but I'm not convinced, do we have hard serialization > against hotplug? Any caller of select_task_rq will check if returned dst_cpu is still working. So there is nothing need worry about. > > > -- Thanks Alex