From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755264Ab1G0VOv (ORCPT ); Wed, 27 Jul 2011 17:14:51 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:33656 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753839Ab1G0VOt (ORCPT ); Wed, 27 Jul 2011 17:14:49 -0400 Date: Wed, 27 Jul 2011 14:14:15 -0700 From: Andrew Morton To: Christoph Hellwig Cc: Dan Ehrenberg , Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] dio: Fast-path for page-aligned IOs Message-Id: <20110727141415.a67cafb8.akpm@linux-foundation.org> In-Reply-To: <20110727210828.GB12714@infradead.org> References: <1308611855-18096-1-git-send-email-dehrenberg@google.com> <20110727210828.GB12714@infradead.org> X-Mailer: Sylpheed 3.0.2 (GTK+ 2.20.1; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 27 Jul 2011 17:08:28 -0400 Christoph Hellwig wrote: > On Mon, Jun 20, 2011 at 04:17:35PM -0700, Dan Ehrenberg wrote: > > The fast path does not apply for operations of the wrong size > > or alignmnent, or for operations on raw drives with 512-byte sectors. > > It might be possible to make this special case a little more general > > while maintaining its performance benefits, but I do not believe that > > the full performance benefits can be achieved without resorting to > > special handling of simple cases, as is done in this patch. > > Did you check how this compares to Andis small optimizations? > > Also operations on raw disks are something people with fast devices > care about a lot. We often hear about benchmark regressions due to > stupid little things in the direct I/O code. > > If we want to special case something that would be a very easy target, > with a 1:1 mapping of logical to physical blocks and thus no need > to call the allocator first, and no need for any kind of locking > or alignment handling. Ken did this back in 2006 (http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=e61c90188b9956edae1105eef361d8981a352fcd) but we reverted that shortly afterwards for some reason.