From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751993AbdF3Deb (ORCPT ); Thu, 29 Jun 2017 23:34:31 -0400 Received: from mail-pf0-f181.google.com ([209.85.192.181]:35979 "EHLO mail-pf0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751888AbdF3De2 (ORCPT ); Thu, 29 Jun 2017 23:34:28 -0400 Date: Fri, 30 Jun 2017 09:04:25 +0530 From: Viresh Kumar To: Dominik Brodowski Cc: Rafael Wysocki , linux-pm@vger.kernel.org, Vincent Guittot , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/6] cpufreq: governor: Drop min_sampling_rate Message-ID: <20170630033425.GU29665@vireshk-i7> References: <713af1a417a9a77f0c41976b25874687ac235e8e.1498733506.git.viresh.kumar@linaro.org> <20170629180123.GA2443@light.dominikbrodowski.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170629180123.GA2443@light.dominikbrodowski.net> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 29-06-17, 20:01, Dominik Brodowski wrote: > On Thu, Jun 29, 2017 at 04:29:06PM +0530, Viresh Kumar wrote: > > The cpufreq core and governors aren't supposed to set a limit on how > > fast we want to try changing the frequency. This is currently done for > > the legacy governors with help of min_sampling_rate. > > > > At worst, we may end up setting the sampling rate to a value lower than > > the rate at which frequency can be changed and then one of the CPUs in > > the policy will be only changing frequency for ever. > > Is it safe to issue requests to change the CPU frequency so frequently, Well, I assumed so. I am not sure the hardware would break though. Overheating ? > even > on historic hardware such as speedstep-{ich,smi,centrino}? In the past, > these checks more or less disallowed the running of dynamic frequency > scaling at least on speedstep-smi[*], We must by doing dynamic freq scaling even without this patch. I don't see why you say the above then. All we do here is that we get rid of the limit on how soon we can change the freq again. > but maybe on a few other platforms as > well. That's why I am curious on whether this may break systems potentially > on a hardware level if the hardware was not designed to do dynamic frequency > scaling (and not just frequency switches on battery/AC). Honestly I am not sure if any hardware can break or not, just because of this commit. -- viresh