From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Tue, 23 Oct 2001 10:05:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 23 Oct 2001 10:05:20 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.101]:12985 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id ; Tue, 23 Oct 2001 10:05:07 -0400 Importance: Normal Subject: Re: [Lse-tech] Re: Preliminary results of using multiblock raw I/O To: Jens Axboe Cc: Reto Baettig , lse-tech@lists.sourceforge.net, linux-kernel@vger.kernel.org X-Mailer: Lotus Notes Release 5.0.3 (Intl) 21 March 2000 Message-ID: From: "Shailabh Nagar" Date: Tue, 23 Oct 2001 10:05:32 -0400 X-MIMETrack: Serialize by Router on D01ML233/01/M/IBM(Release 5.0.8 |June 18, 2001) at 10/23/2001 10:05:32 AM MIME-Version: 1.0 Content-type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org >On Mon, Oct 22 2001, Shailabh Nagar wrote: >> >> >> Unlike the SGI patch, the multiple block size patch continues to use buffer >> heads. So the biggest atomic transfer request that can be seen by a device >> driver with the multiblocksize patch is still 1 page. > >Not so. Given a 1MB contigious request broken into 256 pages, even if >submitted in these chunks it will be merged into the biggest possible >request the lower level driver can handle. This is typically 127kB, for >SCSI it can be as much as 512kB currently and depending on the SCSI >driver even more maybe. My mistake - by device driver I wasn't referring to the lowest level drivers but also including the merging functionality. > >I haven't seen the SGI rawio patch, but I'm assuming it used kiobufs to >pass a single unit of 1 meg down at the time. Yes currently we do incur >significant overhead compared to that approach. > > Getting bigger transfers would require a single buffer head to be able to > point to a multipage buffer or not use buffer heads at all. > The former would obviously be a major change and suitable only for 2.5 > (perhaps as part of the much-awaited rewrite of the block I/O > > Ongoing effort. > > subsystem).The use of multipage transfers using a single buffer head would > also help non-raw I/O transfers. I don't know if anyone is working along > those lines. >It is being worked on. Could you give some idea as to what are some of the ideas being discussed/proposed ? It would be nice to know some of the details as they are being worked on. Thanks, Shailabh Nagar