[openib-general] IPoIB broadcast MC group membership

[Greg Lindahl]

On Tue, Feb 21, 2006 at 11:40:53PM -0800, Fabian Tillier wrote:

> You'd have to make the group 1X.  Note that the group being 1X doesn't
> limit unicast traffic to 1X rates, since the rate for unicast traffic
> would be set based on the rate reported in the path records for the
> various endpoints.
> 
> So 4X SDR and 4X DDR nodes would have to set their inter-packet delay
> for the broadcast group to end up with a 1X packet injection rate.

So, basically, MVAPICH doesn't have code that does either the group
creation properly when there is a mixture of HCA bandwidths, or limit
the packet injection rate. And IPoIB could violate this rule depending
on how user programs use it, e.g. if I did a lot of broadcasting, I
could easily exceed 1X's bandwidth.

So this is more than just a "fix OpenSM" issue. It's more of a "fix
the spec" issue, if I'm understanding it correctly.

-- greg