From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rCstb6pzrzDqDm for ; Mon, 23 May 2016 18:59:51 +1000 (AEST) Received: from foss.arm.com (foss.arm.com [217.140.101.70]) by ozlabs.org (Postfix) with ESMTP id 3rCstb2nRdz9s9n for ; Mon, 23 May 2016 18:59:50 +1000 (AEST) Date: Mon, 23 May 2016 10:00:04 +0100 From: Lorenzo Pieralisi To: Steve Muckle Cc: Peter Zijlstra , 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: <20160523090004.GA21186@red-moon> 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 In-Reply-To: <20160522204252.GH15383@graphite.smuckle.net> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, May 22, 2016 at 01:42:52PM -0700, Steve Muckle wrote: > On Sun, May 22, 2016 at 12:39:12PM +0200, Peter Zijlstra wrote: > > On Fri, May 20, 2016 at 05:53:41PM +0530, Shilpasri G Bhat wrote: > > > > > > Below are the comparisons by disabling watchdog. > > > Both schedutil and ondemand have a similar ramp-down trend. And in both the > > > cases I can see that frequency of the cpu is not reduced in deterministic > > > fashion. In a observation window of 30 seconds after running a workload I can > > > see that the frequency is not ramped down on some cpus in the system and are > > > idling at max frequency. > > > > 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. It is also related to static leakage power that depends on the operating voltage (ie higher operating frequencies require higher voltage) so in a way scaling frequency before going idle may not be effective if voltage does not scale too in turn. Lorenzo