From mboxrd@z Thu Jan 1 00:00:00 1970 From: Prarit Bhargava Subject: Re: [PATCH] cpufreq, intel_pstate, Fix intel_pstate powersave min_perf_pct value Date: Wed, 14 Oct 2015 20:02:02 -0400 Message-ID: <561EECF9.4070500@redhat.com> References: <1444822919-14650-1-git-send-email-prarit@redhat.com> <20151014140957.36523ea9@kcaccard-desk.amr.corp.intel.com> <561EEC6A.7000904@redhat.com> <2038385.VTvETXG82F@vostro.rjw.lan> 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]:47743 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753766AbbJOACE (ORCPT ); Wed, 14 Oct 2015 20:02:04 -0400 In-Reply-To: <2038385.VTvETXG82F@vostro.rjw.lan> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: "Rafael J. Wysocki" Cc: Kristen Carlson Accardi , linux-kernel@vger.kernel.org, Viresh Kumar , linux-pm@vger.kernel.org, Doug Smythies On 10/14/2015 08:29 PM, Rafael J. Wysocki wrote: > On Wednesday, October 14, 2015 07:59:38 PM Prarit Bhargava wrote: >> >> On 10/14/2015 05:09 PM, Kristen Carlson Accardi wrote: >>> On Wed, 14 Oct 2015 07:41:59 -0400 >>> Prarit Bhargava wrote: >>> >>>> On systems that initialize the intel_pstate driver with the performance >>>> governor, and then switch to the powersave governor will not transition to >>>> lower cpu frequencies until /sys/devices/system/cpu/intel_pstate/min_perf_pct >>>> is set to a low value. >>>> >>>> The behavior of governor switching changed after commit a04759924e25 >>>> ("[cpufreq] intel_pstate: honor user space min_perf_pct override on >>>> resume"). The commit introduced tracking of performance percentage >>>> changes via sysfs in order to restore userspace changes during >>>> suspend/resume. The problem occurs because the global values of the newly >>>> introduced max_sysfs_pct and min_sysfs_pct are not lowered on the governor >>>> change and this causes the powersave governor to inherit the performance >>>> governor's settings. >>>> >>>> A simple change would have been to reset max_sysfs_pct to 100 and >>>> min_sysfs_pct to 0 on a governor change, which fixes the problem with >>>> governor switching. However, since we cannot break userspace[1] the fix >>>> is now to give each governor its own limits storage area so that governor >>>> specific changes are tracked. >>>> >>>> I successfully tested this by booting with both the performance governor >>>> and the powersave governor by default, and switching between the two >>>> governors (while monitoring /sys/devices/system/cpu/intel_pstate/ values, >>>> and looking at the output of cpupower frequency-info). Suspend/Resume >>>> testing was performed by Doug Smythies. >>>> >>>> [1] Systems which suspend/resume using the unmaintained pm-utils package >>>> will always transition to the performance governor before the suspend and >>>> after the resume. This means a system using the powersave governor will >>>> go from powersave to performance, then suspend/resume, performance to >>>> powersave. The simple change during governor changes would have been >>>> overwritten when the governor changed before and after the suspend/resume. >>>> I have submitted https://bugzilla.redhat.com/show_bug.cgi?id=1271225 >>>> against Fedora to remove the 94cpufreq file that causes the problem. It >>>> should be noted that pm-utils is obsoleted with newer versions of systemd. >>>> >>>> Cc: Kristen Carlson Accardi >>>> Cc: "Rafael J. Wysocki" >>>> Cc: Viresh Kumar >>>> Cc: linux-pm@vger.kernel.org >>>> Cc: Doug Smythies >>>> Signed-off-by: Prarit Bhargava >>> >>> Acked-by: Kristen Carlson Accardi >>> >>> BTW - I think I can see an issue here with HWP enabled systems. It >>> looks to me like the hwp settings will not be programmed correctly >>> during a governor switch. This probably needs to be addressed in a >>> separate patch. >>> >> >> Oh, I see it now too. I'll get to that in another patch. Thanks for pointing >> that out Kristen. > > The $subject patch doesn't apply any more after the series from Srinivas that > I've just applied. > > Can you please rebase it on top of my bleeding-edge branch? > Sure -- can you send me a pointer to the branch? P. > Thanks, > Rafael >