[openib-general] IB mcast question

[Sean Hefty]

Steve Wise wrote:
> ib_multicast takes care of sending the join/leave info to the SA, right?
> It keeps track of _when_ to leave, for instance.  So since opensm -is-
> getting the join and setting up the group, and the mcast packet is being
> passed to the first member who joined, then I don't think ib_multicast
> can mess up the subsequent members, can it?  

It theory, it shouldn't mess up subsequent members.  While the first join is 
active, subsequent join / leave requests to that same group should be queued. 
After the first join completes, subsequent joins should get a copy of the 
MCMemberRecord that was returned by the SA.

(This is a slight simplification, with the actual operation determined by the 
type of join operation that occurs.  But for the RDMA CM, this is what should 
happen.)

> I'm new to IB mcast, so I'm learning, but it seems like the mthca
> firmware maybe isn't doing the right thing here.  

This was my suspicion, but I couldn't be certain.  It would help if anyone can 
say that they've successfully tested this sort of multicast configuration.  I.e. 
two QPs from the same HCA in the same group.

- Sean