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, 15 Jan 2002 16:23:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Tue, 15 Jan 2002 16:23:30 -0500 Received: from e21.nc.us.ibm.com ([32.97.136.227]:23989 "EHLO e21.nc.us.ibm.com") by vger.kernel.org with ESMTP id ; Tue, 15 Jan 2002 16:23:14 -0500 From: Badari Pulavarty Message-Id: <200201152123.g0FLN6K06540@eng2.beaverton.ibm.com> Subject: Re: [PATCH] O_DIRECT with hardware blocksize alignment To: axboe@suse.de (Jens Axboe) Date: Tue, 15 Jan 2002 13:23:06 -0800 (PST) Cc: andrea@suse.de (Andrea Arcangeli), jlbec@evilplan.org (Joel Becker), marcelo@conectiva.com.br (Marcelo Tosatti), linux-kernel@vger.kernel.org (lkml) In-Reply-To: <20020115145549.M31878@suse.de> from "Jens Axboe" at Jan 15, 2002 01:55:49 PM PST X-Mailer: ELM [version 2.5 PL3] MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Wouldn't this cause, single IO to split into (possibly) 3 I/Os for RAW VARY on all unaligned IOs ? In that case, wouldn't it be better of doing entire I/O with 512byte buffer heads, so that all of them can be merged ? IMHO, preventing the merge due to b_size mismatch just to handle few drivers/hardware may be overkill. This will penalize all the drivers which can handle variable size IOs also. Isn't it ? Leaving it to the driver and doing variable size I/O on only the drivers that can handle them, may be a better option ? In my initial version of RAW VARY patch, I split the I/Os into possibly 3 I/O in raw.c. Do brw_kiovec(.., 512) for the first page and last pages & 4K for the middle pages. It showed reduction in CPU utilization for large IOs. But it since it could split single I/O into 3 I/Os, i did not see significant I/O throughput improvement. Regards, Badari > > On Tue, Jan 15 2002, Jens Axboe wrote: > > On Tue, Jan 15 2002, Andrea Arcangeli wrote: > > > actually we could also forbid merging at the ll_rw_block layer if b_size > > > is not equal, maybe that's the simpler solution to that problem after > > > all, merging between kiovec I/O and buffered I/O probably doesn't > > > matter. > > > > Agreed, this is also what I suggested. > > Here's the right version, sorry. This still potentially decrements > elevator sequence wrongly for a missed front merge, but that's an issue > I can definitely live with :-) > ....