From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755234Ab1G0VIe (ORCPT ); Wed, 27 Jul 2011 17:08:34 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:52512 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753875Ab1G0VIb (ORCPT ); Wed, 27 Jul 2011 17:08:31 -0400 Date: Wed, 27 Jul 2011 17:08:28 -0400 From: Christoph Hellwig To: Dan Ehrenberg Cc: Alexander Viro , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] dio: Fast-path for page-aligned IOs Message-ID: <20110727210828.GB12714@infradead.org> References: <1308611855-18096-1-git-send-email-dehrenberg@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1308611855-18096-1-git-send-email-dehrenberg@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.