[openib-general] A critique of RDMA PUT/GET in HPC

[Greg Lindahl]

On Fri, Aug 25, 2006 at 10:13:01AM -0500, Tom Tucker wrote:

> He does say this, but his analysis does not support this conclusion. His
> analysis revolves around MPI send/recv, not the MPI 2.0 get/put
> services.

Nobody uses MPI put/get anyway, so leaving out analyzing that doesn't
change reality much.

> A valid conclusion IMO is that "MPI send/recv can
> be most efficiently implemented over an unconnected reliable datagram
> protocol that supports 64bit tag matching at the data sink." And not
> coincidentally, Myricom has this ;-)

As do all of the non-VIA-family interconnects he mentions.  Since "we"
all landed on the same conclusion, you might think we're on to
something. Or not.

However, that's only part of the argument.  Another part is that the
buffer space needed to use RDMA put/get for all data links is huge.
And there are some other interesting points.

> I DO agree that it is interesting reading. :-), it's definitely got
> people fired up.

Heh. Glad you found it interesting.

-- greg