Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756889Ab3DZPqb (ORCPT ); Fri, 26 Apr 2013 11:46:31 -0400 Received: from mga14.intel.com ([143.182.124.37]:26015 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756817Ab3DZPq1 (ORCPT ); Fri, 26 Apr 2013 11:46:27 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,559,1363158000"; d="scan'208";a="293659683" Message-ID: <517AA14D.7060202@linux.intel.com> Date: Fri, 26 Apr 2013 08:46:21 -0700 From: Arjan van de Ven User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 MIME-Version: 1.0 To: Vincent Guittot CC: linux-kernel , LAK , "linaro-kernel@lists.linaro.org" , Peter Zijlstra , Ingo Molnar , Russell King - ARM Linux , Paul Turner , Santosh , Morten Rasmussen , Chander Kashyap , "cmetcalf@tilera.com" , "tony.luck@intel.com" , Alex Shi , Preeti U Murthy , Paul McKenney , Thomas Gleixner , Len Brown , Amit Kucheria , Jonathan Corbet , Lukasz Majewski Subject: Re: [RFC PATCH v4 00/14] sched: packing small tasks References: <1366910611-20048-1-git-send-email-vincent.guittot@linaro.org> <517A969B.5040606@linux.intel.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1907 Lines: 39 >> >> >> so I got to ask the hard question; what percentage of system level (not just >> cpu level) >> power consumption gain can you measure (pick your favorite workload)... >> > > I haven't system level figures for my patches but only for the cpu > subsystem. If we use the MP3 results in the back of my mail, they show > an improvement of 37 % (113/178) for the CPU subsystem of the > platform. If we assume that the CPU subsystem contributes 25% of an > embedded system power consumption (this can vary across platform > depending of the use of HW accelerator but it should be a almost fair > percentage), the patch can impact the power consumption on up to 9%. > sadly the math tends to not work quite that easy; memory takes significantly more power when the system is not idle than when it is idle for example. [*] so while reducing cpu power by making it run a bit longer (at lower frequency or slower core or whatever) is a pure win if you only look at the cpu, but it may (or may not) be a loss when looking at a whole system level. I've learned the hard way that you cannot just look at the cpu numbers; you must look at the whole-system power when playing with such tradeoffs. That does not mean that your patch is not useful; it very well can be, but without having looked at whole-system power that's a very dangerous conclusion to make. So.. if you get a chance, I'd love to see data on a whole-system level... even for just one workload and one system (playing mp3 sounds like a quite reasonable workload for such things indeed) [*] I assume that on your ARM systems, memory goes into self refresh during system idle just as it does on x86 -- 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/