From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753909AbcEWJYe (ORCPT ); Mon, 23 May 2016 05:24:34 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:60055 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753845AbcEWJYc (ORCPT ); Mon, 23 May 2016 05:24:32 -0400 Date: Mon, 23 May 2016 11:24:16 +0200 From: Peter Zijlstra To: Steve Muckle Cc: Daniel Lezcano , Shilpasri G Bhat , "Rafael J. Wysocki" , Viresh Kumar , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List , "Gautham R. Shenoy" , shreyas@linux.vnet.ibm.com, akshay.adiga@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org Subject: Re: [RFC PATCH] Increase in idle power with schedutil Message-ID: <20160523092416.GE15728@worktop.ger.corp.intel.com> References: <1463576020-18597-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com> <20160519114029.GW3193@twins.programming.kicks-ass.net> <201605201223.u4KCNWn9028105@mx0a-001b2d01.pphosted.com> <20160522103912.GN3193@twins.programming.kicks-ass.net> <20160522204252.GH15383@graphite.smuckle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160522204252.GH15383@graphite.smuckle.net> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, May 22, 2016 at 01:42:52PM -0700, Steve Muckle wrote: > > So does it actually matter what the frequency is when you idle? Isn't > > the whole thing clock gated anyway? > > > > Because this seems to generate contradictory requirements, on the one > > hand we want to stay idle as long as possible while on the other hand > > you seem to want to clock down while idle, which requires not being > > idle. > > > > If it matters; should not your idle state muck explicitly set/restore > > frequency? > > AFAIK this is very platform dependent. Some will waste more power than > others when a CPU idles above fmin due to things like resource (bus > bandwidth, shared cache freq etc) voting. Oh agreed, completely platform dependent. 'Luckily' all this cpuidle is already very platform dependent. > It is also true that there is power spent going to fmin (and then > perhaps restoring the frequency when idle ends) which will be in part a > function of how slow the frequency change operation is on that platform. Agreed. > I think Daniel Lezcano (added) was exploring the idea of having cpuidle > drivers take the expected idle duration and potentially communicate to > cpufreq to reduce the frequency depending on a platform-specific > cost/benefit analysis. Right; that's along the lines I was thinking. If the idle guestimate and the idle QoS both allow (ie. it wins on power and doesn't violate wake-up latency) muck with DVSF on the idle path.