Return-Path: Received: from quartz.orcorp.ca ([184.70.90.242]:43547 "EHLO quartz.orcorp.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752030AbbGXWin (ORCPT ); Fri, 24 Jul 2015 18:38:43 -0400 Date: Fri, 24 Jul 2015 16:38:35 -0600 From: Jason Gunthorpe To: Steve Wise Cc: dledford@redhat.com, infinipath@intel.com, sagig@mellanox.com, ogerlitz@mellanox.com, roid@mellanox.com, linux-rdma@vger.kernel.org, eli@mellanox.com, target-devel@vger.kernel.org, linux-nfs@vger.kernel.org, bfields@fieldses.org Subject: Re: [PATCH V6 9/9] isert: Support iWARP transports using FRMRs Message-ID: <20150724223835.GA29064@obsidianresearch.com> References: <20150724161331.25617.8475.stgit@build2.ogc.int> <20150724161904.25617.85015.stgit@build2.ogc.int> <20150724165721.GC25480@obsidianresearch.com> <00ce01d0c641$493ea300$dbbbe900$@opengridcomputing.com> <20150724192411.GC26225@obsidianresearch.com> <00db01d0c64b$01f40300$05dc0900$@opengridcomputing.com> <00ee01d0c65d$a1e03cf0$e5a0b6d0$@opengridcomputing.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <00ee01d0c65d$a1e03cf0$e5a0b6d0$@opengridcomputing.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Jul 24, 2015 at 05:11:04PM -0500, Steve Wise wrote: > By the way, just to be clear: If you use a FRWR, you by definition > only have one SGE entry as the result of the registration. So > regardless of what a device/protocol can do with the destination SGE > of an RDMA READ operation, if you use FRWR to register the > destination region, you need only 1 SGE in the RDMA READ WR. FRWR's have horrible restrictions on the scatterlist. To realize arbitrary scatterlists requires multiple MRs, and thus multiple SGE entries. The warning is for a reader who might be familiar with IB and think iWarp simply needs to have a MR wrapped around the memory and assume gaps/etc can be supported through a s/g list, like IB can. Jason