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Subject: Re: [OMPI users] OpenMPI extremely slow with progress threads
From: tomek (t.koziara_at_[hidden])
Date: 2009-08-21 12:18:02


Hi Jeff

I am using OMPI on a MacBook Pro (for the moment).

> What's "extremely slowly", and what does your test program do?

For example, test programs of Zoltan (load balancing library from
sandia) never finish, while normally
they take a fraction of second to finish.

> By "asynchronous progress", do you mean that you used the --enable-
> progress-threads option to OMPI's configure, or that you are using
> non-blocking MPI function calls?

I meant using --enable-progress-threads. When disabled - doesn't it
mean that block and non-blocking communication are basically same (and
blocking)? (at least on a gigabit ethernet TCPIP based network)

> I'd say that the progress threads stuff in OMPI is immature at
> best. At worst, it may crash. It's likely very untested.

Yes, I could see that myself.

> The non-blocking function calls should work just as well as the
> blocking function calls -- depending on your application, hardware,
> communication patterns, etc., you can get significant speedup by
> using the non-blocking communication calls.

I am not very knowledgeable in terms of networking, but is gigabit
ethernet/TCPIP capable of asynchronous comm?

> FWIW, some types of networks effectively have asynchronous progress
> anyway (which is one of the reasons we haven't done too much on the
> OMPI software side of enabling async. progress). If your network
> has hardware (or software) offload of message passing, then you
> might be getting it "for free" by OMPI's normal operating modes
> anyway. Note that asynchronous progress is typically most useful
> when sending large messages.

Will need to learn more and see on which from the available clusters
should I be able to have good support for asynch. which is needed in
my application.