Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754671AbcKJANw (ORCPT ); Wed, 9 Nov 2016 19:13:52 -0500 Received: from mail-qt0-f176.google.com ([209.85.216.176]:33814 "EHLO mail-qt0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751725AbcKJANu (ORCPT ); Wed, 9 Nov 2016 19:13:50 -0500 MIME-Version: 1.0 In-Reply-To: <20161109055537.GA5544@vireshk-i7> References: <076fb177-9cb3-4534-aadb-ebc2190d0751@email.android.com> <5ea3831e-7743-d39f-1f02-96c915cc757e@semaphore.gr> <20161109055537.GA5544@vireshk-i7> From: "Rafael J. Wysocki" Date: Thu, 10 Nov 2016 01:13:49 +0100 X-Google-Sender-Auth: _6tsOJxM038YMntiP0M5TPy5-bI Message-ID: Subject: Re: [Resend][PATCH] cpufreq: conservative: Decrease frequency faster when the timer deferred To: Viresh Kumar Cc: Stratos Karafotis , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , "Rafael J. Wysocki" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 46 On Wed, Nov 9, 2016 at 6:55 AM, Viresh Kumar wrote: > On 08-11-16, 21:25, Stratos Karafotis wrote: >> But this is the supposed behaviour of conservative governor. We want >> the CPU to increase the frequency in steps. The patch just resets >> the frequency to a lower frequency in case of idle. >> >> For argument's sake, let's assume that the governor timer is never >> deferred and runs every sampling period even on completely idle CPU. > > There are no timers now :) > >> And let's assume, for example, a burst load that runs every 100ms >> for 20ms. The default sampling rate is also 20ms. >> What would conservative do in case of that burst load? It would >> increase the frequency by one freq step after 20ms and then it would >> decrease the frequency 4 times by one frequency step. Most probably >> on the next burst load, the CPU will run on min frequency. >> >> I agree that maybe this is not ideal for performance but maybe this is >> how we want conservative governor to work (lazily increase and decrease >> frequency). > > Idle periods are already accounted for while calculating system load by legacy > governors. > > And the more and more I think about this, I am inclined towards your patch. > Maybe in a bit different form and commit log. > > If we see how the governors were written initially, there were no deferred > timers. And so even if CPUs were idle, we will wake up to adjust the step. > > Even if we want to make the behavior similar to that, then also we should > account of missed sampling periods both while decreasing or increasing > frequencies. > > @Rafael: What do you think ? It looks like the issue with the conservative governor is real, but I'm a bit concerned about adding things to use by one particular governor only to cpufreq_governor.c. Apart from the timer-related terminology that is not applicable any more, of course. Thanks, Rafael