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Subject: Re: [OMPI users] OpenMPI extremely slow with progress threads
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-08-20 08:47:08


On Aug 19, 2009, at 7:48 PM, tomek wrote:

> Now that I have complied my code with OpenMPI 1.3.3 here is a new
> problem:
>
> When asynchronous progress is enabled even a simplest test problems
> run extremely slowly.
>

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

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

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.

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.

-- 
Jeff Squyres
jsquyres_at_[hidden]