[ewg] Using ib_send_bw for multicast performance test

[Kovacs Peter Tamas]

Hi all,

I'm trying to benchmark multicast performance on a simple Infiniband 
network with three nodes using ib_send_bw, but apparently we cannot find 
the right parameters for doing so.
Point-to-point measurements work fine, but when setting up a multicast 
test with one sender and multiple receivers, we cannot make them start. 
The best
I guess it must be something like "ib_send_bw -c UD -g <some number> " 
on the sender side, and "ib_send_bw -c UD" on the receivers side, but I 
don't know how the senders and receivers can all connect to exchange 
data, like they do in a point-to-point test by providing the IP address 
of the listening end.

Skimming through the source, ctx_hand_shake looks to me like it's for 
two parties, not more than two, but I must be wrong. The readme also 
talks about a single server and a single client. As far as I can see, I 
cannot list multiple IPs when using the multicast feature either. The 
best I could make is an "Failed to exchange date between server and 
clients" error message, making one of the listening servers exit.
I've got predefined multicast groups from 0xc000 to 0xc0009, and queried 
the corresponding GIDs with saquery, but feeding any of these via the -M 
option did not help either.

Could any of you please shed some light about using this feature, ie. 
measuring multicast performance between 1+N nodes, one sender and N 
receivers.

With many thanks,
Peter Kovacs