Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751953Ab3GPGPT (ORCPT ); Tue, 16 Jul 2013 02:15:19 -0400 Received: from mail-oa0-f47.google.com ([209.85.219.47]:42885 "EHLO mail-oa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751594Ab3GPGPQ (ORCPT ); Tue, 16 Jul 2013 02:15:16 -0400 MIME-Version: 1.0 In-Reply-To: <51E3C950.90503@linux.vnet.ibm.com> References: <20130711221419.547.69781.stgit@srivatsabhat.in.ibm.com> <20130711221704.547.64296.stgit@srivatsabhat.in.ibm.com> <51E3C950.90503@linux.vnet.ibm.com> Date: Tue, 16 Jul 2013 11:45:16 +0530 Message-ID: Subject: Re: [PATCH 7/8] cpufreq: Preserve policy structure across suspend/resume From: Viresh Kumar To: "Srivatsa S. Bhat" Cc: rjw@sisk.pl, toralf.foerster@gmx.de, robert.jarzmik@intel.com, durgadoss.r@intel.com, tianyu.lan@intel.com, lantianyu1986@gmail.com, dirk.brandewie@gmail.com, stern@rowland.harvard.edu, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1832 Lines: 41 On 15 July 2013 15:35, Srivatsa S. Bhat wrote: > Actually even I was wondering about this while writing the patch and > I even tested shutdown after multiple suspend/resume cycles, to verify that > the refcount is messed up. But surprisingly, things worked just fine. > > Logically there should've been a refcount mismatch and things should have > failed, but everything worked fine during my tests. Apart from suspend/resume > and shutdown tests, I even tried mixing a few regular CPU hotplug operations > (echo 0/1 to sysfs online files), but nothing stood out. > > Sorry, I forgot to document this in the patch. Either the patch is wrong > or something else is silently fixing this up. Not sure what is the exact > situation. To understand it I actually applied your patches to get better view of the code. (Haven't tested it though).. And found that your code is doing the right thing and we shouldn't get a mismatch.. This is the sequence of events I can draw: - __cpu_add_dev() for first cpu. sets the refcount to 'x', where x are the no. of cpus in its clock domain. - _cpu_add_dev() for other cpus: doesn't change anything in refcount - Suspend: - cpu_remove_dev() for all cpus, due to frozen flag we don't touch the value of count - Resume: - cpu_add_dev() for all cpus, due to frozen flag we don't touch the value of count. And so things work as expected. That's why your code isn't breaking anything I believe. But can no. of cpus change inbetween suspend/resume? Then count would be tricky as we are using the same policy structure. -- 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/