From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3rCtQy4cwRzDqDv for ; Mon, 23 May 2016 19:24:26 +1000 (AEST) Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2001:1868:205::9]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3rCtQy2Pvdz9sds for ; Mon, 23 May 2016 19:24:26 +1000 (AEST) 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 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: > > 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.