From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753188Ab3H0ReT (ORCPT ); Tue, 27 Aug 2013 13:34:19 -0400 Received: from sema.semaphore.gr ([78.46.194.137]:47231 "EHLO sema.semaphore.gr" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1752618Ab3H0ReS (ORCPT ); Tue, 27 Aug 2013 13:34:18 -0400 Message-ID: <521CE317.20908@semaphore.gr> Date: Tue, 27 Aug 2013 20:34:15 +0300 From: Stratos Karafotis User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8 MIME-Version: 1.0 To: Viresh Kumar CC: "Rafael J. Wysocki" , "cpufreq@vger.kernel.org" , "linux-pm@vger.kernel.org" , LKML Subject: Re: [PATCH] cpufreq: governors: Remove duplicate check of target freq in supported range References: <521BA068.8030003@semaphore.gr> <521CC9B8.2020801@semaphore.gr> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 08/27/2013 07:07 PM, Viresh Kumar wrote: > On 27 August 2013 21:16, Stratos Karafotis wrote: >> I think we should keep these checks because: >> >> 1) They shorten the execution code (there is no unnecessary call of >> __cpufreq_driver_target) > > I don't really count this one.. This is how code is present everywhere in > kernel.. These checks are present in routines and callers don't need to > take care of them.. I mean that if we will get rid of the code you mentioned, we will have an extra call to function __cpufreq_driver_target in some cases. >> 2) In case my patch will be accepted, we need them to avoid continuously >> increase of dbs_info->requested_freq.With my patch the requested_freq >> can temporarily overcome policy->min and policy->max. __cpufreq_driver_target >> will select the correct frequency (within policy->min and policy->max). >> Then, dbs_cpufreq_notifier will adjust requested_freq. > > Sorry, I couldn't understand what you meant here :( > I'm sorry. Let me try to explain this better. With my patch, dbs_info->requested_freq will not be capped within policy->min and policy->max in cs_check_cpu. So, temporarily it may have a value greater than policy->max or lower that policy->min. When we call __cpufreq_driver_target, the correct frequency will be selected because __cpufreq_driver_target takes care to adjust the target frequency within policy range. But, eventually, dbs_cpufreq_notifier will adjust dbs_info->requested within policy range, if needed. If we remove if (dbs_info->requested_freq == policy->max) return; and if (policy->cur == policy->min) return; request_freq will keep increasing or decreasing in each iteration and finally will overflow or underflow. Consider, for example, that in a CPU with policy->max = 1000MHz the current frequency is 950MHz. With a constant load above up_threshold, the requested_freq in first iteration will be 1000MHz and __cpufreq_driver_target will select 1000MHz freq. In second iteration, requested_freq will be 1050MHz, and __cpufreq_driver_target will select 1000MHz. dbs_cpufreq_notifier will adjust requested_freq back to 1000MHz. In next iterations, dbs_cpufreq_notifier will not be called, so we need the above check (dbs_info->requested_freq == policy->max) to prevent requested_freq to grow arbitrary. I hope my explanation was better now. :) Thanks, Stratos