From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752568Ab2LKEYE (ORCPT ); Mon, 10 Dec 2012 23:24:04 -0500 Received: from e28smtp01.in.ibm.com ([122.248.162.1]:49851 "EHLO e28smtp01.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751487Ab2LKEYC (ORCPT ); Mon, 10 Dec 2012 23:24:02 -0500 Message-ID: <50C6B530.3030307@linux.vnet.ibm.com> Date: Tue, 11 Dec 2012 09:53:12 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:14.0) Gecko/20120717 Thunderbird/14.0 MIME-Version: 1.0 To: Alex Shi CC: rob@landley.net, mingo@redhat.com, peterz@infradead.org, gregkh@linuxfoundation.org, andre.przywara@amd.com, rjw@sisk.pl, paul.gortmaker@windriver.com, akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, linux-kernel@vger.kernel.org, pjt@google.com, vincent.guittot@linaro.org Subject: Re: [PATCH 01/18] sched: select_task_rq_fair clean up References: <1355127754-8444-1-git-send-email-alex.shi@intel.com> <1355127754-8444-2-git-send-email-alex.shi@intel.com> In-Reply-To: <1355127754-8444-2-git-send-email-alex.shi@intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12121104-4790-0000-0000-000005F83FF3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Alex, On 12/10/2012 01:52 PM, Alex Shi wrote: > It is impossible to miss a task allowed cpu in a eligible group. The one thing I am concerned with here is if there is a possibility of the task changing its tsk_cpus_allowed() while this code is running. i.e find_idlest_group() finds an idle group,then the tsk_cpus_allowed() for the task changes,perhaps by the user himself,which might not include the cpus in the idle group.After this find_idlest_cpu() is called.I mean a race condition in short.Then we might not have an eligible cpu in that group right? > And since find_idlest_group only return a different group which > excludes old cpu, it's also imporissible to find a new cpu same as old > cpu. This I agree with. > Signed-off-by: Alex Shi > --- > kernel/sched/fair.c | 5 ----- > 1 files changed, 0 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 59e072b..df99456 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -3150,11 +3150,6 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags) > } > > new_cpu = find_idlest_cpu(group, p, cpu); > - if (new_cpu == -1 || new_cpu == cpu) { > - /* Now try balancing at a lower domain level of cpu */ > - sd = sd->child; > - continue; > - } > > /* Now try balancing at a lower domain level of new_cpu */ > cpu = new_cpu; > Regards Preeti U Murthy