From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756066AbaCFEnN (ORCPT ); Wed, 5 Mar 2014 23:43:13 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58339 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755948AbaCFEnL (ORCPT ); Wed, 5 Mar 2014 23:43:11 -0500 Date: Wed, 5 Mar 2014 20:43:37 -0800 From: Greg KH To: Jon Ringle Cc: "Ringle, Jonathan" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] Add option to build with -O3 Message-ID: <20140306044337.GB5722@kroah.com> References: <1393977709-9809-1-git-send-email-jringle@gridpoint.com> <20140305050927.GA8534@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.22 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 05, 2014 at 02:32:26AM -0500, 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? > > (Resending this message, since it was "destroyed". Hopefully, this is now > an an acceptable form :) > > 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. I'd take this up with the linux-arm developers, that sounds like something is wrong with your system that a compiler change fixes problems. Something else must be wrong... good luck, greg k-h