[Mpi3-subsetting] agenda for subsetting kickoff telecon ww09

[Torsten Hoefler]

Hi,
> Thanks. As soon as there's a couple of non-blocking recvs out there,
> waiting for them in reverse order requires tracking of the moment when
> the receives were posted. In some cases this leads to extra fields and
> data exchanges.
How's that different from multiple Recvs in multiple threads. Hmm, I
guess the threaded case is just undefined and the implementation is
allowed to ignore ordering, right? 

> The footprint argument generally says that the library will be smaller.
> This may be a minor matter for general purpose computers, but as soon as
> you go to Petascale, you need every byte on the compute nodes for user
> data, especially if dynamic libraries are not supported.
ack

> As for the collectives, many are implemented using SendRecv, and that
> blocking call in turn often uses non-blocking communication. Classic
> Alltoallv algorithm uses nonblocking calls, too. So, I'm not sure that
> even unoptimized blocking collectives will always use only blocking
> pt2pt.
Yes, of course - again, the proposed "interface" is more of a logical
nature. You can implement all blocking collectives with blocking p2p
(it'll be slower). But ok, pulling all p2p functions in this interface
is also unproblematic. So I don't really have a srong opinion here.

Best,
  Torsten


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