Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756953Ab0HGHbU (ORCPT ); Sat, 7 Aug 2010 03:31:20 -0400 Received: from mtagate7.uk.ibm.com ([194.196.100.167]:36082 "EHLO mtagate7.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752568Ab0HGHbR (ORCPT ); Sat, 7 Aug 2010 03:31:17 -0400 Message-ID: <4C5D0BC2.1040706@linux.vnet.ibm.com> Date: Sat, 07 Aug 2010 09:31:14 +0200 From: Christian Ehrhardt User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.1.11) Gecko/20100713 Thunderbird/3.0.6 MIME-Version: 1.0 To: Christoph Hellwig CC: Josef Bacik , Andrew Morton , "linux-kernel@vger.kernel.org" , linux-fsdevel@vger.kernel.org, linux-btrfs@vger.kernel.org Subject: Re: PATCH 3/6 - direct-io: do not merge logically non-contiguous requests References: <4C5BE8DB.5030503@linux.vnet.ibm.com> <20100806120358.GA31601@infradead.org> In-Reply-To: <20100806120358.GA31601@infradead.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1375 Lines: 36 On 08/06/2010 02:03 PM, Christoph Hellwig wrote: > Something is deeply wrong here. Raw block device access has a 1:1 > mapping between logical and physical block numbers. They really should > never be non-contiguous. At least I did nothing I know about to break it :-) As I mentioned just iozone using direct I/O (-I flag of iozone then using O_DIRECT for the file) on a ext2 file-system. The file system was coming clean out of mkfs the file was written with iozone one step before the traced read run. The only uncommon thing here might be the block device, which is a scsi disk on our SAN servers (I'm running on s390) - so the driver in charge is zfcp (drivers/s390/scsi/). I could use dasd (drivers/s390/block) disks as well, but I have no blktrace of them yet - what I already know is that they show a similar cost increase. On monday I should be able to get machine resources to verify that both disk types are affected. Let me know if I can do anything else on my system to shed some light on the matter. -- Gr?sse / regards, Christian Ehrhardt IBM Linux Technology Center, System z Linux Performance -- 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/