Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753423AbaFHHaY (ORCPT ); Sun, 8 Jun 2014 03:30:24 -0400 Received: from mga01.intel.com ([192.55.52.88]:1889 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753317AbaFHHaX (ORCPT ); Sun, 8 Jun 2014 03:30:23 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.98,997,1392192000"; d="scan'208";a="551990872" Date: Sun, 8 Jun 2014 07:26:29 +0800 From: Yuyang Du To: Peter Zijlstra Cc: Dirk Brandewie , "Rafael J. Wysocki" , Morten Rasmussen , "linux-kernel@vger.kernel.org" , "linux-pm@vger.kernel.org" , "mingo@kernel.org" , "vincent.guittot@linaro.org" , "daniel.lezcano@linaro.org" , "preeti@linux.vnet.ibm.com" , Dietmar Eggemann , len.brown@intel.com, jacob.jun.pan@linux.intel.com Subject: Re: [RFC PATCH 06/16] arm: topology: Define TC2 sched energy and provide it to scheduler Message-ID: <20140607232628.GC22261@intel.com> References: <1400869003-27769-1-git-send-email-morten.rasmussen@arm.com> <20140604160230.GS29593@e103034-lin> <20140604172712.GJ13930@laptop.programming.kicks-ass.net> <2484761.vkWavnsDx3@vostro.rjw.lan> <20140605065205.GA3213@twins.programming.kicks-ass.net> <539086B3.2010804@gmail.com> <20140605202930.GA15484@intel.com> <20140606080543.GR6758@twins.programming.kicks-ass.net> <20140606003520.GB22261@intel.com> <20140606105036.GQ3213@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140606105036.GQ3213@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 06, 2014 at 12:50:36PM +0200, Peter Zijlstra wrote: > > Voltage is combined with frequency, roughly, voltage is proportional > > to freuquecy, so roughly, power is proportionaly to voltage^3. You > > P ~ V^2, last time I checked. > > > can't say which is more important, or there is no reason to raise > > voltage without raising frequency. > > Well, some chips have far fewer voltage steps than freq steps; or, > differently put, they have multiple freq steps for a single voltage > level. > > And since the power (Watts) is proportional to Voltage squared, its the > biggest term. > > If you have a distinct voltage level for each freq, it all doesn't > matter. > Ok. I think we understand each other. But one more thing, I said P ~ V^3, because P ~ V^2*f and f ~ V, so P ~ V^3. Maybe some frequencies share the same voltage, but you can still safely assume V changes with f in general, and it will be more and more so, since we do need finer control over power consumption. > Sure, but realize that we must fully understand this governor and > integrate it in the scheduler if we're to attain the goal of IPC/watt > optimized scheduling behaviour. > Attain the goal of IPC/watt optimized? I don't see how it can be done like this. As I said, what is unknown for prediction is perf scaling *and* changing workload. So the challenge for pstate control is in both. But I see more chanllenge in the changing workload than in the performance scaling or the resulting IPC impact (if workload is fixed). Currently, all freq governors take CPU utilization (load%) as the indicator (target), which can server both: workload and perf scaling. As for IPC/watt optimized, I don't see how it can be practical. Too micro to be used for the general well-being? > So you (or rather Intel in general) will have to be very explicit on how > their stuff works and can no longer hide in some driver and do magic. > The same is true for all other vendors for that matter. > > If you (vendors, not Yuyang in specific) do not want to play (and be > explicit and expose how your hardware functions) then you simply will > not get power efficient scheduling full stop. > > There's no rocks to hide under, no magic veils to hide behind. You tell > _in_public_ or you get nothing. Better communication is good, especially for our increasingly iterated products because the changing products do incur noises and inconsistency in detail. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/