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Subject: Re: [OMPI users] Performance: MPICH2 vs OpenMPI
From: Eugene Loh (Eugene.Loh_at_[hidden])
Date: 2008-10-08 19:00:39


Eugene Loh wrote:

> Sangamesh B wrote:
>
>> The job is run on 2 nodes - 8 cores.
>>
>> OpenMPI - 25 m 39 s.
>> MPICH2 - 15 m 53 s.
>
> I don't understand MPICH very well, but it seemed as though some of
> the flags used in building MPICH are supposed to be added in
> automatically to the mpicc/etc compiler wrappers.

Again, this may not apply to your case, but I found out some more
details on my theory.

If you build MPICH2 like this:

    % configure CFLAGS=-O2
    % make

then when you use "mpicc" to build your application, you automatically
get that optimization flag built in.

What had confused me was that I tried confirming the theory by building
MPICH2 like this:

    % configure --enable-fast
    % make

That does *NOT* up the mpicc optimization level (despite their
documentation).