Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755932AbYGMTqV (ORCPT ); Sun, 13 Jul 2008 15:46:21 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754579AbYGMTqL (ORCPT ); Sun, 13 Jul 2008 15:46:11 -0400 Received: from 74-93-104-97-Washington.hfc.comcastbusiness.net ([74.93.104.97]:54485 "EHLO sunset.davemloft.net" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1754599AbYGMTqK (ORCPT ); Sun, 13 Jul 2008 15:46:10 -0400 Date: Sun, 13 Jul 2008 12:46:10 -0700 (PDT) Message-Id: <20080713.124610.193703496.davem@davemloft.net> To: andi@firstfloor.org Cc: mpatocka@redhat.com, sparclinux@vger.kernel.org, linux-kernel@vger.kernel.org, jens.axboe@oracle.com Subject: Re: [SUGGESTION]: drop virtual merge accounting in I/O requests From: David Miller In-Reply-To: <487A083F.9010301@firstfloor.org> References: <87iqvb2skz.fsf@basil.nowhere.org> <487A083F.9010301@firstfloor.org> X-Mailer: Mew version 5.2 on Emacs 22.1 / Mule 5.0 (SAKAKI) 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 Content-Length: 737 Lines: 18 From: Andi Kleen Date: Sun, 13 Jul 2008 15:50:55 +0200 > Still I would expect that modern IO controllers are typically fast > enough at processing SG lists that it shouldn't matter much. I know it matters a lot on sparc64 ESP scsi controllers. You can only have one address/len pair DMA'ing at a time and you have to service an interrupt to load in the the next DMA sg elements into the chips registers. Merging is essentially a must for performance on those cards. -- 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/