Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754965AbXFVI3V (ORCPT ); Fri, 22 Jun 2007 04:29:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751806AbXFVI3N (ORCPT ); Fri, 22 Jun 2007 04:29:13 -0400 Received: from arx.rabbit.us ([68.251.127.6]:4559 "EHLO arx.rabbit.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751810AbXFVI3M (ORCPT ); Fri, 22 Jun 2007 04:29:12 -0400 Message-ID: <467B8855.1030007@rabbit.us> Date: Fri, 22 Jun 2007 10:29:09 +0200 From: Peter Rabbitson User-Agent: Mozilla-Thunderbird 2.0.0.4 (X11/20070618) MIME-Version: 1.0 To: Robert Hancock CC: linux-kernel@vger.kernel.org Subject: Re: Terrible IO performance when using 4GB of RAM on a 32 bit machine References: <467B1100.4000401@shaw.ca> In-Reply-To: <467B1100.4000401@shaw.ca> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1703 Lines: 41 Robert Hancock wrote: > Peter Rabbitson wrote: >> H. Peter Anvin wrote: >>> >>> What does /proc/mtrr look like in the two cases? >>> >> >> Identical for mem=3900 and without it. >> >> reg00: base=0x00000000 ( 0MB), size=2048MB: write-back, count=1 >> reg01: base=0x80000000 (2048MB), size=1024MB: write-back, count=1 >> reg02: base=0xc0000000 (3072MB), size= 512MB: write-back, count=1 >> reg03: base=0xe0000000 (3584MB), size= 256MB: write-back, count=1 >> reg04: base=0xf0000000 (3840MB), size= 128MB: write-back, count=1 >> reg05: base=0xf8000000 (3968MB), size= 32MB: write-back, count=1 > > Looks like another case of bad MTRRs on an Intel motherboard? The BIOS > is marking only memory up to 4000MB as cacheable, but the actual memory > extends up to about 4031MB. Therefore anything that accesses the top > 31MB of memory will run very slow. > Ah, it all makes sense now. In this case I assume mem=4000 is perfectly safe and usable for the time being. In the beginning I tried with mem=4g, which obviously did not work. If anyone is interested in adding an exception/workaround for this particular motherboard, I'd be happy to help with testing. I have added more information about the system: current kernel config [1], output of `lspci -vv`[2], dmesg with mem=4000[3]. Thank you! Peter [1] http://rabbit.us/pool/4g/config-2.6.21.5.arzamas.6.txt [2] http://rabbit.us/pool/4g/lspci_4000.txt [3] http://rabbit.us/pool/4g/dmesg_4000.txt - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/