From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752306AbaCGMvx (ORCPT ); Fri, 7 Mar 2014 07:51:53 -0500 Received: from mail-ig0-f172.google.com ([209.85.213.172]:39645 "EHLO mail-ig0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751487AbaCGMvw (ORCPT ); Fri, 7 Mar 2014 07:51:52 -0500 Message-ID: <5319C0EC.3040606@gmail.com> Date: Fri, 07 Mar 2014 07:51:56 -0500 From: Austin S Hemmelgarn User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Richard Weinberger , Borislav Petkov , Jon Ringle CC: Greg KH , "Ringle, Jonathan" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] Add option to build with -O3 References: <1393977709-9809-1-git-send-email-jringle@gridpoint.com> <20140305050927.GA8534@kroah.com> <5319BE19.5000607@gmail.com> <5319BEC0.4050006@nod.at> In-Reply-To: <5319BEC0.4050006@nod.at> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2014-03-07 07:42, Richard Weinberger wrote: > > > Am 07.03.2014 13:39, schrieb Austin S Hemmelgarn: >> On 2014-03-06 08:28, Richard Weinberger wrote: >>> On Wed, Mar 5, 2014 at 6:37 AM, Jon Ringle >>> wrote: >>>> >>>> >>>> On Wed, 5 Mar 2014, Greg KH wrote: >>>> >>>>> On Tue, Mar 04, 2014 at 07:01:49PM -0500, Jon Ringle wrote: >>>>>> +config CC_OPTIMIZE_FOR_SPEED + bool "Optimze for speed >>>>>> (-O3)" + help + Enabling this option will pass "-O3" >>>>>> to gcc + resulting in a larger kernel (but possibly >>>>>> faster) >>>>> >>>>> Are you sure about that? Have you measured it? >>>> >>>> I do know that there is an improvement performance-wise for my >>>> particular use-case. >>>> >>>> My target is an ARM board being built with gcc-4.8.2. My board >>>> has on it a sc16is740 that is used as an RS-485 port. The >>>> sc16is740 is on the i2c bus, so when an interrupt comes in to >>>> indicate that there is data available to be read, I need to get >>>> the data over the i2c bus. I do this on a kthread to do this >>>> work. The i2c transactions (using i2c-davinci driver) are also >>>> interrupt driven. I was seeing a lot of lost packets when >>>> receiving data at only 19200. Adding the -O3 compile option >>>> helped in this regard in that I am now rarely seeing packet >>>> loss. >>> >>> Please also see: >>> http://www.gossamer-threads.com/lists/linux/kernel/1835761?do=post_view_threaded#1835761 >>> >>> >> Ironically, combining these might achieve a significant performance >> improvement over CONFIG_GENERIC_CPU and -O2. > > *might* > We still need a sane proof. > > Thanks, > //richard > I'm not arguing that, I just don't have the time to test it at the moment; and, "performance improvement" also can mean different things to different people (a lot of RT folks for example don't care if things run faster if it makes them much less deterministic).