[openib-general] IB mcast question

[Steve Wise]

On Tue, 2006-08-15 at 09:58 -0700, Sean Hefty wrote:
> >The qkeys used by the RDMA CM sound like they may be the problem.  I'll verify
> >this and see how to fix it if so.
> 
> If I set the qkeys for the QPs and MCMemberRecord to 0, I can get this to work
> now.  The RDMA CM uses a qkey = port number for UD QPs, and a qkey = IPv4
> address for MCMemberRecords.
> 
> A potential fix I see for this is to use the same qkey for all UD QPs and
> multicast groups created by the RDMA CM.  Otherwise we restrict UD QPs to using
> a single destination (remote UD QP or multicast group.)
> 

I was marching to the same tune!  But I have a few points needing
clarification.

In my IP-centric mind, the sender specifies the ip mcast address and a
remote port.  All hosts with subscribers to the ip mcast address get the
packet, and all sockets on those hosts who are bound to the dst_port
receive a copy.   Other sockets on those hosts that joined the ipmcast
group but are bound to different ports will _not_ get a copy of the
packet.  In addition, the sender's local port number doesn't matter at
all in the equation.   Now how does that translate to qkeys, udqops, and
ib mcast?

It sounds to me like the remote_qkey is used to identify the mcast group
when sending a mcast -and- to identify the set of qps on each host that
should receive the incoming mcast packets.  Is this true?