[openib-general] RFC MPI and app. requirements of OpenIB

[Hal Rosenstock]

On Thu, 2005-12-22 at 14:34, Sean Hefty wrote:
> >I'm soliciting feedback from the MPI and other application developers regarding
> >which OpenIB APIs they will be targeting with their implementations.
> >Specifically, myself and some of the other IB developers are interesting in
> >knowing if userspace applications will be written to the RDMA CMA interface,
> >the
> >IB CM API, or some other abstraction.
> 
> To help clarify the trade-offs:
> 
> The CMA allows the use of IP addressing for connection establishment and
> abstracts device hotplug.  It also operates over any type of RDMA device.
> 
> A disadvantage of using the CMA is that it may not select the best set of paths
> between two or more nodes.

What defines best ? Is this preference or disjointedness or something
else ?

Note path selection may be important in subnets when LMC > 0.

>   The IB CM also permits path failover on a single
> HCA.  Use of the IB CM requires that clients also interface with the IB SA to
> obtain path records.

Note that interaction with the SA will be required for MPI when
multicast groups are to be used.

> My personal recommendation would be for applications to use the CMA, but that
> does result in losing some flexibility.

Would the CMA ultimately support path failover ?

-- Hal