From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754251AbaGaW65 (ORCPT ); Thu, 31 Jul 2014 18:58:57 -0400 Received: from mx1.redhat.com ([209.132.183.28]:7035 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753305AbaGaW6y (ORCPT ); Thu, 31 Jul 2014 18:58:54 -0400 Message-ID: <53DACA26.1000908@redhat.com> Date: Thu, 31 Jul 2014 18:58:46 -0400 From: Prarit Bhargava User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20131028 Thunderbird/17.0.10 MIME-Version: 1.0 To: Saravana Kannan CC: "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Viresh Kumar , Lenny Szubowicz , linux-pm@vger.kernel.org Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] References: <1406634362-811-1-git-send-email-prarit@redhat.com> <2066166.pXm4lKLOID@vostro.rjw.lan> <53DA8389.80804@redhat.com> <1917362.abr2Y4p7vh@vostro.rjw.lan> <53DA8A41.2030601@redhat.com> <53DAA60B.6040802@codeaurora.org> <53DAA749.5080506@redhat.com> <53DAA95B.2040505@codeaurora.org> <53DAB038.3050007@redhat.com> <53DABFA6.6090503@codeaurora.org> In-Reply-To: <53DABFA6.6090503@codeaurora.org> 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 07/31/2014 06:13 PM, Saravana Kannan wrote: > On 07/31/2014 02:08 PM, Prarit Bhargava wrote: >> >> >> On 07/31/2014 04:38 PM, Saravana Kannan wrote: >>> On 07/31/2014 01:30 PM, Prarit Bhargava wrote: >>>> >>>> >>>> On 07/31/2014 04:24 PM, Saravana Kannan wrote: >>>>> >>>>> Prarit, >>>>> >>>>> I'm not an expert on sysfs locking, but I would think the specific sysfs lock >>>>> would depend on the file/attribute group. So, can you please try to hotplug a >>>>> core in/out (to trigger the POLICY_EXIT) and then read a sysfs file >>>>> exported by >>>>> the governor? scaling_governor doesn't cut it since that file is not >>>>> removed on >>>>> policy exit event to governor. If it's ondemand, try reading/write it's >>>>> sampling >>>>> rate file. >>>> >>>> Thanks Saravana -- will do. I will get back to you shortly on this. >>>> >>> >>> Thanks. Btw, in case you weren't already aware of it. You'll have to hoplug out >>> all the CPUs in a cluster to trigger a POLICY_EXIT for that cluster/policy. >> >> Yep -- the affected_cpus file should show all the cpus in the policy IIRC. One >> of the systems I have has 1 cpu/policy and has 48 threads so the POLICY_EXIT is >> called. >> >> I'll put something like >> >> while [1]; >> do >> echo ondemand > /sys/devices/system/cpu/cpu1/cpufreq/scaling_governor >> cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> echo 20000 > /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> cat /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate >> echo 0 > /sys/devices/system/cpu/cpu1/online >> sleep 1 >> echo 1 > /sys/devices/system/cpu/cpu1/online >> sleep 1 >> done >> > > The actual race can only happen with 2 threads. I'm just trying to trigger a > lockdep warning here. I ran the above in two separate terminals with cpuset -c 0 and cpuset -c 1 to multi-thread it all. No deadlock or LOCKDEP trace after about 1/2 hour, so I think we're in the clear on that concern. P.