Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263107AbUC2TqW (ORCPT ); Mon, 29 Mar 2004 14:46:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263120AbUC2TqU (ORCPT ); Mon, 29 Mar 2004 14:46:20 -0500 Received: from parcelfarce.linux.theplanet.co.uk ([195.92.249.252]:24204 "EHLO www.linux.org.uk") by vger.kernel.org with ESMTP id S263107AbUC2TqK (ORCPT ); Mon, 29 Mar 2004 14:46:10 -0500 Message-ID: <40687CF0.3040206@pobox.com> Date: Mon, 29 Mar 2004 14:45:52 -0500 From: Jeff Garzik User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.4) Gecko/20030703 X-Accept-Language: en-us, en MIME-Version: 1.0 To: Andrea Arcangeli CC: Bartlomiej Zolnierkiewicz , Jens Axboe , William Lee Irwin III , Nick Piggin , linux-ide@vger.kernel.org, Linux Kernel , Andrew Morton Subject: Re: [PATCH] speed up SATA References: <4066021A.20308@pobox.com> <200403282030.11743.bzolnier@elka.pw.edu.pl> <20040328183010.GQ24370@suse.de> <200403282045.07246.bzolnier@elka.pw.edu.pl> <406720A7.1050501@pobox.com> <20040329005502.GG3039@dualathlon.random> <40679FE3.3080007@pobox.com> <20040329130410.GH3039@dualathlon.random> In-Reply-To: <20040329130410.GH3039@dualathlon.random> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1322 Lines: 31 Andrea Arcangeli wrote: > Once you change the API too, then you can set the hardwre limit in your > driver and relay on the highlevel blkdev code to find the optimal runtime > dma size for bulk I/O, but today it's your driver that is enforcing a > runtime bulk dma size, not the maximim limit of the controller, and so > you should code your patch accordingly. This magic 512k or 1M limit has nothing to do with SATA. It's a magic number whose definition is "we don't want PATA or SATA or SCSI disks doing larger requests than this for latency, VM, and similar reasons." That definition belongs outside the low-level SATA driver. This 512k/1M value is sure to change over time, which involves needlessly plugging the same value into multiple places. And when such changes occurs, you must be careful not to exceed hardware- and errata-based limits -- of which there is no distinction in the code. I think the length of this discussion alone clearly implies that the low-level driver should not be responsible for selecting this value, if nothing else ;-) Jeff - 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/