[openib-general] IPoIB broadcast MC group membership

[Hal Rosenstock]

On Wed, 2006-02-22 at 14:54, Fabian Tillier wrote:
> 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.

You can also get rate information on multicast groups too from the SA.

-- Hal

> Hopefully that helps.
> 
> - Fab
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