Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757445AbXFVOid (ORCPT ); Fri, 22 Jun 2007 10:38:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755849AbXFVOiY (ORCPT ); Fri, 22 Jun 2007 10:38:24 -0400 Received: from shawidc-mo1.cg.shawcable.net ([24.71.223.10]:2025 "EHLO pd4mo1so.prod.shaw.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755525AbXFVOiX (ORCPT ); Fri, 22 Jun 2007 10:38:23 -0400 Date: Fri, 22 Jun 2007 08:36:58 -0600 From: Robert Hancock Subject: Re: Terrible IO performance when using 4GB of RAM on a 32 bit machine In-reply-to: <467B8855.1030007@rabbit.us> To: Peter Rabbitson Cc: linux-kernel@vger.kernel.org Message-id: <467BDE8A.8040609@shaw.ca> MIME-version: 1.0 Content-type: text/plain; charset=UTF-8; format=flowed Content-transfer-encoding: 7bit References: <467B1100.4000401@shaw.ca> <467B8855.1030007@rabbit.us> User-Agent: Thunderbird 2.0.0.4 (Windows/20070604) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1980 Lines: 49 Peter Rabbitson wrote: > 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 There was a patch floating around recently to detect the case where the MTRRs don't map all of RAM as write-back, automatically cap the memory used by the kernel to what is mapped and print some loud warnings.. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from hancockr@nospamshaw.ca Home Page: http://www.roberthancock.com/ - 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/