[openib-general] IB mcast question

[Hal Rosenstock]

Steve,
 
IB only replicates once per node (and also not on the incoming port if there are any members).
 
The SM tracks join states (full, non member, send only member) for a port. It doesn't matter whether the SM gets duplicated join requests for a port. It would just indicate that was OK and the node would still only get one packet per send from another port in that group. It's up to the HCA to replicate the multicast packet to all its QPs which are part of that group.
 
-- Hal

________________________________

From: openib-general-bounces at openib.org on behalf of Steve Wise
Sent: Mon 8/14/2006 4:18 PM
To: Roland Dreier
Cc: openib-general
Subject: Re: [openib-general] IB mcast question



On Mon, 2006-08-14 at 12:42 -0700, Roland Dreier wrote:
>     Steve> However, if I run 2 instances of the app that reads mcasts
>     Steve> and dumps them to stdout, I only get the mcast packets
>     Steve> delivered to one of the applications.  Namely the first one
>     Steve> who joins the group seems to get the mcasts.  I know for
>     Steve> UDP/IP multicast, all applications bound to the same port
>     Steve> and joined to the IP mcast addr will get a copy of incoming
>     Steve> mcast packets.  Is this not true for IB mcast?  It appears
>     Steve> not based on my tests...
>
> This should work -- multicast packets should be replicated to all
> attached UD QPs.  There is likely a bug in the librdma multicast support.
>

So is this replicating done in the mthca hca? 

Since one app is getting the mcast packet, can I assume the opensm code
is doing the right thing switch/port wise?

Should the SM get join requests for both applications that join the
group on the same host?  Or only the first one?

Steve.




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