From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753516Ab3BUBfa (ORCPT ); Wed, 20 Feb 2013 20:35:30 -0500 Received: from mga14.intel.com ([143.182.124.37]:10122 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753277Ab3BUBf3 (ORCPT ); Wed, 20 Feb 2013 20:35:29 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,705,1355126400"; d="scan'208";a="204692300" Message-ID: <512579F6.4080800@intel.com> Date: Thu, 21 Feb 2013 09:35:50 +0800 From: Alex Shi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120912 Thunderbird/15.0.1 MIME-Version: 1.0 To: Peter Zijlstra CC: torvalds@linux-foundation.org, mingo@redhat.com, tglx@linutronix.de, akpm@linux-foundation.org, arjan@linux.intel.com, bp@alien8.de, pjt@google.com, namhyung@kernel.org, efault@gmx.de, vincent.guittot@linaro.org, gregkh@linuxfoundation.org, preeti@linux.vnet.ibm.com, viresh.kumar@linaro.org, linux-kernel@vger.kernel.org, morten.rasmussen@arm.com Subject: Re: [patch v5 06/15] sched: log the cpu utilization at rq References: <1361164062-20111-1-git-send-email-alex.shi@intel.com> <1361164062-20111-7-git-send-email-alex.shi@intel.com> <1361352643.10155.4.camel@laptop> <5124DED5.5050207@intel.com> <1361373631.10155.40.camel@laptop> In-Reply-To: <1361373631.10155.40.camel@laptop> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/20/2013 11:20 PM, Peter Zijlstra wrote: > On Wed, 2013-02-20 at 22:33 +0800, Alex Shi wrote: >>> There's generally a better value than 100 when using computers.. >> seeing >>> how 100 is 64+32+4. >> >> I didn't find a good example for this. and no idea of your suggestion, >> would you like to explain a bit more? > > Basically what you're doing ends up being fixed point math, using 100 as > unit is inefficient, pick a power-of-2 and everything reduces to > bit-shifts. > > http://en.wikipedia.org/wiki/Fixed-point_arithmetic > > So use 128 or 1024 or whatever and you don't need mult and div > instructions to represent [0,1] > got it. will reconsider this. -- Thanks Alex