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Re: MPI defaults



Am Samstag, den 14.03.2009, 10:54 +0100 schrieb Francesco P. Lovergine:
> while working on HDF5 I'm considering to move MPI support to use mpi-default-dev
> and mpi-default-bin. That would imply providing a single reference platform support
> (openmpi or lam, completely dropping mpich AFAIK) which is quite different from what
> done until today. I wonder if it would be appropriate having instead a mpi-all-dev and
> mpi-any-bin package which depends on all supported platforms
> on every archs. That would allow transparently building lam, mpich and openmpi 
> flavors whenever possible, and depending on any appropriate tool the admin would install.

That is probably the goal to go for but there are some technical
problems with it. Most debian/rules can't easily include a snippet and
finally do the right thing.

There are also some other issues: Most MPI implementations do not play
well together, meaning there currently are problems if two or more are
installed. (Yes, there shouldn't be, but it's an unresolved issue as of
now.) Also, LAM/MPI can be considered to be dead upstream and is not
recommended for usage, I think Debian should not build against it
anymore; there's nothing against still providing the libraries, of
course. Also, MPICH is superseeded by MPICH2 which noone ever packaged.
I do not know the details but as I check last, MPICH2 seems to not have
support for modern inter-conntects. They are supported via forks, so one
would have to package a MPICH2 version for each interconnect.

Mpi-defaults was supposed to support package who need MPI support, and
give it to them in an easy way. I was not designed to be a full-blown
solution. it definitely worth for such a solution but several questions
need to be addressed first. I do maintain a list of issues that in my
opinion need to be resolved first. I need to write it up in a better way
and have it discussed here and in pkg-scicomp first. Also, we should
check if we really want so many (and out-dated) MPI versions in Debian,
of if we can go with one for the apps and provide libs for all others.
If MPI were to be standardized on ABI compatibility, that resolve the
whole issue. But since this is not going to happen anytime soon, we have
to work on a solution that works for us.

I really welcome your idea and would be glad to hear suggestions if you
have an idea of how to implement that! I also hope we can have the
discussion about MPI in Debian soon; but I currently have to spend the
time to fix "my" MPI implementation before I can write up a proposal.

Best regards
Manuel

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