[Mpi3-subsetting] agenda for subsetting kickoff telecon ww09

[Jeff Squyres]

One other issue is that we'd have to make [at least some of] the  
MPI_Info_* functions be able to be called before MPI_INIT.

On Feb 29, 2008, at 3:54 PM, Supalov, Alexander wrote:

> Hi,
>
> Thanks. I was thinking privately about MPI_Init_subsets or so that  
> would
> use an Info object, too. I bet a comparable idea - or at least  
> desire to
> keep the number of subset related calls under strict control - was  
> aired
> at the telecon by someone, but we didn't go into much detail then.
>
> One reservation I have about Info objects is that they are so flexible
> as to be dangerous. They promoting lots of optional, loosely  
> controlled
> features that can effectively blur the interface definition. On the
> other hand, I don't see any viable alternative to that, at least if  
> the
> number of subsets is going to be substantial and ever growing.
>
> Of course, it's a little too early to fix any implementation details  
> I'm
> afraid. Anyway, let's keep this idea in mind while we're settling the
> scope.
>
> Best regards.
>
> Alexander
>
> -----Original Message-----
> From: mpi3-subsetting-bounces_at_[hidden]
> [mailto:mpi3-subsetting-bounces_at_[hidden]] On Behalf Of Jeff
> Squyres
> Sent: Friday, February 29, 2008 9:29 PM
> To: mpi3-subsetting_at_[hidden]
> Subject: Re: [Mpi3-subsetting] agenda for subsetting kickoff telecon
> ww09
>
> 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
>
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-- 
Jeff Squyres
Cisco Systems