Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756112AbYBRJnt (ORCPT ); Mon, 18 Feb 2008 04:43:49 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751774AbYBRJnj (ORCPT ); Mon, 18 Feb 2008 04:43:39 -0500 Received: from fwil.voltaire.com ([193.47.165.2]:18298 "EHLO exil.voltaire.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751368AbYBRJnh (ORCPT ); Mon, 18 Feb 2008 04:43:37 -0500 Message-ID: <47B95343.9060802@Voltaire.COM> Date: Mon, 18 Feb 2008 11:43:31 +0200 From: Erez Zilber User-Agent: Mozilla-Thunderbird 2.0.0.9 (X11/20080110) MIME-Version: 1.0 To: Bart Van Assche CC: FUJITA Tomonori , rdreier@cisco.com, James.Bottomley@hansenpartnership.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, vst@vlnb.net, linux-scsi@vger.kernel.org, scst-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: Integration of SCST in the mainstream Linux kernel References: <1201639331.3069.58.camel@localhost.localdomain> <20080130083239E.fujita.tomonori@lab.ntt.co.jp> <47A89660.1080804@Voltaire.COM> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 18 Feb 2008 09:43:35.0383 (UTC) FILETIME=[BB162E70:01C87212] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1663 Lines: 41 Bart Van Assche wrote: > On Feb 5, 2008 6:01 PM, Erez Zilber wrote: > >> Using such large values for FirstBurstLength will give you poor >> performance numbers for WRITE commands (with iSER). FirstBurstLength >> means how much data should you send as unsolicited data (i.e. without >> RDMA). It means that your WRITE commands were sent without RDMA. >> > > Sorry, but I'm afraid you got this wrong. When the iSER transport is > used instead of TCP, all data is sent via RDMA, including unsolicited > data. If you have look at the iSER implementation in the Linux kernel > (source files under drivers/infiniband/ulp/iser), you will see that > all data is transferred via RDMA and not via TCP/IP. > > When you execute WRITE commands with iSCSI, it works like this: EDTL (Expected data length) - the data length of your command FirstBurstLength - the length of data that will be sent as unsolicited data (i.e. as immediate data with the SCSI command and as unsolicited data-out PDUs) If you use a high value for FirstBurstLength, all (or most) of your data will be sent as unsolicited data-out PDUs. These PDUs don't use the RDMA engine, so you miss the advantage of IB. If you use a lower value for FirstBurstLength, EDTL - FirstBurstLength bytes will be sent as solicited data-out PDUs. With iSER, solicited data-out PDUs are RDMA operations. I hope that I'm more clear now. Erez -- 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/