From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: [PATCH] cpufreq, store_scaling_governor requires policy->rwsem to be held for duration of changing governors [v2] Date: Thu, 31 Jul 2014 17:08:08 -0400 Message-ID: <53DAB038.3050007@redhat.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.redhat.com ([209.132.183.28]:61665 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752779AbaGaVIO (ORCPT ); Thu, 31 Jul 2014 17:08:14 -0400 In-Reply-To: <53DAA95B.2040505@codeaurora.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Saravana Kannan Cc: "Rafael J. Wysocki" , linux-kernel@vger.kernel.org, Viresh Kumar , Lenny Szubowicz , linux-pm@vger.kernel.org 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 and let it run unless you can think of something else. FWIW, manually trying that yields no problems AFAICT. The sleeps are just me being paranoid and keeping things in sequence. P. > > -Saravana >