From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-out.m-online.net (mail-out.m-online.net [212.18.0.10]) by ozlabs.org (Postfix) with ESMTP id 00573B7CB6 for ; Wed, 24 Mar 2010 06:44:04 +1100 (EST) To: =?UTF-8?B?TsOpbWV0aCBNw6FydG9u?= From: Wolfgang Denk Subject: Re: Linux patches for XIP on MPC8xx? MIME-Version: 1.0 Content-type: text/plain; charset=ISO-8859-1 In-reply-to: <4BA865D4.1090403@freemail.hu> References: <4BA865D4.1090403@freemail.hu> Date: Tue, 23 Mar 2010 20:44:01 +0100 Message-Id: <20100323194401.0B7724C022@gemini.denx.de> Cc: linuxppc-dev Development , Wolfgang Grandegger List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Dear Márton Németh, in message <4BA865D4.1090403@freemail.hu> you wrote: > > I found your homepage at > http://www.denx.de/wiki/bin/view/DULG/ConfigureLinuxForXIP back > from 2003. Was there any follow up of your patch for kernel 2.4.4? There were very few tests done with later kernel versions, and in all practical system configurations we tested we found that XIP did not give real benefits. Usually execution from flash was slower than when running from RAM, and even booting a (inevitably uncompressed) kernel from flash is typically slower than loading a compressed image to RUM and booting from there. So except for some highly specialized applications (you may also call these "exotic" configurations) XIP for the Linux kernel does not make much sense to me. I am aware that there are reports which come to completely different conclusions - see for example http://www.elinux.org/Kernel_XIP ; but then look carefully - the examples come from hardware with really slow processors, which are probably not typical any more. Actually this is the first thing you should check: the ratio of processor speed versus flash memory bandwidth versus RAM bandwidth. Today you can usually expect CPU clocks way over 400 MHz, and many systems use DDR, while NOR flash speed has noch changed much. Also check if it is possible to map the flash memory cached for your system (which you definitly want when using XIP from flash); this may prevent some flash access methods from working. Best regards, Wolfgang Denk -- DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd@denx.de Doubt isn't the opposite of faith; it is an element of faith. - Paul Tillich, German theologian and historian