Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762923AbXLMSgU (ORCPT ); Thu, 13 Dec 2007 13:36:20 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754492AbXLMSgH (ORCPT ); Thu, 13 Dec 2007 13:36:07 -0500 Received: from rtr.ca ([76.10.145.34]:2060 "EHLO mail.rtr.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753036AbXLMSgD (ORCPT ); Thu, 13 Dec 2007 13:36:03 -0500 Message-ID: <47617B92.6020908@rtr.ca> Date: Thu, 13 Dec 2007 13:36:02 -0500 From: Mark Lord User-Agent: Thunderbird 2.0.0.9 (X11/20071031) MIME-Version: 1.0 To: Jens Axboe , IDE/ATA development list , Linux Kernel , linux-scsi Subject: QUEUE_FLAG_CLUSTER: not working in 2.6.24 ? Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1187 Lines: 29 Jens, I'm experimenting here with trying to generate large I/O through libata, and not having much luck. The limit seems to be the number of hardware PRD (SG) entries permitted by the driver (libata:ata_piix), which is 128 by default. The problem is, the block layer *never* sends an SG entry larger than 8192 bytes, and even that size is exceptionally rare. Nearly all I/O segments are 4096 bytes, so I never see a single I/O larger than 512KB (128 * 4096). If I patch various parts of block and SCSI, this limit doesn't budge, but when I change the hardware PRD limit in libata, it scales by exactly whatever I set the new value to. This tells me that adjacent I/O segments are not being combined. I thought that QUEUE_FLAG_CLUSTER (aka. SCSI host .use_clustering=1) should result in adjacent single pages being combined into larger physical segments? This is x86-32 with latest 2.6.24-rc*. I'll re-test on older kernels next. ??? -- 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/