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Subject: Re: [OMPI users] difference between single and double precision
From: Eugene Loh (eugene.loh_at_[hidden])
Date: 2010-12-06 10:31:40

Mathieu Gontier wrote:

> Nevertheless, one can observed some differences between MPICH and
> OpenMPI from 25% to 100% depending on the options we are using into
> our software. Tests are lead on a single SGI node on 6 or 12
> processes, and thus, I am focused on the sm option.

Is it possible to narrow our focus here a little? E.g., are there
particular MPI calls that are much more expensive with OMPI than MPICH?
Is the performance difference observable with simple ping-pong tests?

> So, I have two questions:
> 1/ does the option--mca mpool_sm_max_size=XXXX can change something (I
> am wondering if the value is not too small and, as consequence, a set
> of small messages is sent instead of a big one)

There was recent related discussion on this mail list.

Check the OMPI FAQ for more info. E.g.,

This particular parameter disappeared with OMPI 1.3.2.

To move messages as bigger chunks, try btl_sm_eager_limit and

> 2/ is there a difference between --mca btl tcp,sm,self and --mca btl
> self,sm,tcp (or not put any explicit mca option)?

I think tcp,sm,self and self,sm,tcp will be the same. Without an
explicit MCA btl choice, it depends on what BTL choices are available.