From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752699AbaCGMjv (ORCPT ); Fri, 7 Mar 2014 07:39:51 -0500 Received: from mail-ie0-f180.google.com ([209.85.223.180]:54561 "EHLO mail-ie0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751082AbaCGMju (ORCPT ); Fri, 7 Mar 2014 07:39:50 -0500 Message-ID: <5319BE19.5000607@gmail.com> Date: Fri, 07 Mar 2014 07:39:53 -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 , 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> In-Reply-To: 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 2014-03-06 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.