Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752961AbaGaWOE (ORCPT ); Thu, 31 Jul 2014 18:14:04 -0400 Received: from smtp.codeaurora.org ([198.145.11.231]:59402 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750789AbaGaWOA (ORCPT ); Thu, 31 Jul 2014 18:14:00 -0400 Message-ID: <53DABFA6.6090503@codeaurora.org> Date: Thu, 31 Jul 2014 15:13:58 -0700 From: Saravana Kannan User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130329 Thunderbird/17.0.5 MIME-Version: 1.0 To: Prarit Bhargava 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> In-Reply-To: <53DAB038.3050007@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed 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 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. -Saravana -- The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation -- 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/