[openib-general] IPoIB broadcast MC group membership

[Fabian Tillier]

On 2/22/06, amith rajith mamidala <mamidala at cse.ohio-state.edu> wrote:
>
> I have a question related to the mixture of HCA bandwidths
> in the fabric. For an upper layer, like MVAPICH, "negotiating"
> for a rate so that all the ports are "involved" can be quite
> expensive, especially if the code falls in the critical path.
> Can any additional support be provided by the underlying
> SA interface, so that the upper protocal layers can do the job
> in a minimum time. This kind of support can be used not only for
> MPI but for other stacks as well,

All the rate information can be figured out at process launch time. 
If at launch time each MPI process used the SA to query for path
information to connect to all the other processes, then the
application could also look at the returned set of paths and figure
out what the slowest rate in the fabric is and use that for multicast
traffic.  Note that point-to-point traffice, whether reliable
connected or unreliable datagram, would use the rate in the path
record returned by the SA.  Only multicast traffic must be aware of
the rate limitations of the whole job.

Hopefully that helps.

- Fab