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 <jlayton@xxxxxxxxxx> > >>>--- > >>> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
