Return-Path: Received: from fieldses.org ([173.255.197.46]:41262 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751165AbdBWUMY (ORCPT ); Thu, 23 Feb 2017 15:12:24 -0500 Date: Thu, 23 Feb 2017 15:11:09 -0500 From: "J. Bruce Fields" To: Tom Talpey Cc: Jeff Layton , trond.myklebust@primarydata.com, schumaker.anna@gmail.com, linux-nfs@vger.kernel.org, Chuck Lever , linux-rdma@vger.kernel.org Subject: Re: [PATCH 1/4] sunrpc: flag transports as using IETF approved congestion control protocols Message-ID: <20170223201109.GC11882@fieldses.org> References: <20170223170337.10686-1-jlayton@redhat.com> <20170223170337.10686-2-jlayton@redhat.com> <2152dfdf-f847-2511-1600-6499b6ea9708@talpey.com> <1487880034.3448.8.camel@redhat.com> <65056db6-f30a-c44d-b01c-b549887c4895@talpey.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <65056db6-f30a-c44d-b01c-b549887c4895@talpey.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: On Thu, Feb 23, 2017 at 03:06:25PM -0500, Tom Talpey wrote: > On 2/23/2017 3:00 PM, Jeff Layton wrote: > >On Thu, 2017-02-23 at 14:42 -0500, Tom Talpey wrote: > >>On 2/23/2017 12:03 PM, Jeff Layton wrote: > >>>Signed-off-by: Jeff Layton > >>>--- > >>> include/linux/sunrpc/svc_xprt.h | 1 + > >>> net/sunrpc/svcsock.c | 1 + > >>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 2 ++ > >> > >>There's a possibly-important detail here. Not all RDMA transports have > >>"IETF-approved congestion control", for example, RoCEv1. However, iWARP > >>and (arguably) RoCEv2 do. On the other hand, as a nonroutable protocol, > >>RoCEv1 may not fall under this restriction. > >> > >>Net-net, inspecting only the RDMA attribute of the transport may be > >>insufficient here. > >> > >>It could be argued however that the xprtrdma layer, with its rpcrdma > >>crediting, provides such congestion. But that needs to be made > >>explicit, and perhaps, discussed in IETF. Initially, I think it would > >>be important to flag this as a point for the future. For now, it may > >>be best to flag RoCEv1 as not supporting congestion. > >> > >>Tom. > >> > > > >(cc'ing Chuck and the linux-rdma list) > > > >Thanks Tom, that's very interesting. > > > >Not being well versed in the xprtrdma layer, what condition should we > >use here to set the flag? git grep shows that the string "ROCEV1" only > >shows up in the bxnt_en driver. Is there some way to determine this > >generically for any given RDMA driver? > > I would not code RoCEv1 as an exception, I would code iWARP and RoCEv2 > as the only eligible ones. There are any number of other possibilities, > none of which should be automatically flagged as congestion-controlled. > > I'm also not sure I'm comfortable with hardcoding such a list into RPC. > But it may be the best you can do for now. Chuck, are you aware of a > verbs interface to obtain the RDMA transport type? If this gets too complicated--we've been allowing NFSv4/UDP for years, letting this one (arguable?) exception through in RDMA a little longer won't kill us. (And if we really shouldn't be doing NFSv4 over some RDMA transports--is it worth supporting them at all, if the only support we can get is NFSv3-only?) --b.