[Mpi3-subsetting] agenda for subsetting kickoff telecon ww09

[Jeff Squyres]

On Feb 28, 2008, at 11:29 PM, Supalov, Alexander wrote:

> - Communicator & group management: better memory footprint.

Take this point to an extreme - it may be possible to say "this app  
only uses MPI_COMM_WORLD".  In this case, you can remove the  
communicator field from network packets for a small gain in latency,  
or perhaps reduce it from 4 to 2 bytes or 1 byte (e.g., if an app says  
"I'll only use 4 communicators").

> - Message tagging: better support for stable dataflow exchanges,  
> smaller
> packets.

Two points here:

- allow app to eliminate MPI_ANY_TAG
- just like with communicators, allow the app to say "I'll only use N  
tags", where N can save you space in network packets (e.g., if N==1,  
no need for tag on the wire; if N == 2, then you only need 1 byte for  
the tag, etc.).

> - Non-blocking communication: easier ordering, simplified request
> handling.

If there is no non-blocking communication, enormous chunks of the  
progression engine can be optimized in terms of memory (i.e., remove  
lots of now-unnecessary code) and probably a little speed.

On the teleconf (sorry I missed it), was there discussion of how to  
specify these hints?  Perhaps a new function: MPI_INIT_INFO (pass an  
MPI_Info handle to MPI_INIT)?  Or is it something that needs to be  
specified at compile/link time?


-- 
Jeff Squyres
Cisco Systems