Re: MPICH as default MPI; WAS: MPI debugging workflows

[Alastair McKinstry <alastair.mckinstry@sceal.ie>]

On 11/12/2018 18:26, Drew Parsons wrote:
> On 2018-12-08 12:31, Drew Parsons wrote:
> > On 2018-12-07 19:49, Alastair McKinstry wrote:
> > > > >
> > > Looking into it further, I'm reluctant now to move to mpich for buster
> > > as the default. One was the experience of the openmpi3 transition,
> > > shaking out many issues.
> ...
> > > So I think more testing of mpich3 builds with CH4 /pmix / OFI support
> > > is needed, but moving over openmpi-> mpich at this stage is iffy.
> >
> >
> > Thanks Alistair, your analysis sounds sound.  I'm happy to be patient
> > with the switch and wait till after buster, especially if pmix support
> > complicates the matter.  That will make it all the more useful to set
> > up a test buildd to test the transition.
> >
> > I'll invite upstream authors who have been promoting mpich over
> > openmpi to chip in with their experience.
>
> I received this feedback from a PETSc developer:
>
>   "The Open MPI API is better for developers due to better type safety 
> (all
>   handles in MPICH are typedef'd to int). Most major commercial vendors
>   are organized around variants of MPICH (where there is collective ABI
>   standardization). Open MPI is more modular so most vendor stuff goes
>   into their plugins (for those vendors working with OMPI).
>
>   "I think a good solution for Linux distros (and many others) would 
> be to
>   make a library that is ABI compatible with OMPI, but dispatches through
>   to MPICH.  There exists a (messy) open source demonstration.
>
>   "  https://github.com/cea-hpc/wi4mpi/ "
>
>
>
> ABI compatibility sounds like a nice resolution of the dilemma.
>
>
> Drew
Thanks, thats interesting. Yes, we should work for ABI compatibility for 
Bullseye.

My goals for MPI in Bullseye are:

(1) symbol versioning. OpenMPI has just released 4.0, but its too late 
to realistically push into Buster given experience. I have a symbol 
versioning patch that upstream have tentatively agreed to but needs work 
for non-gcc compilers. I intend to get that into the OpenMPI5 release, 
and OpenMPI5 into Bullseye, aiming to  make that the "last" big OpenMPI 
transition ...

(2) Ditto for MPICH ?

(3) Build using pkg-confiig instead of mpicc / mpifort wrappers. As of 
now, OpenMPI and MPICH are multiarch-aware, so you can cross-build MPI 
applications, but only if you use pkg-config rather than mpi wrappers.  
Push this work through the MPI stack.

Best regards

Alastair



--
Alastair McKinstry, <alastair@sceal.ie>, <mckinstry@debian.org>, https://diaspora.sceal.ie/u/amckinstry
Commander Vimes didn’t like the phrase “The innocent have nothing to fear,”
 believing the innocent had everything to fear, mostly from the guilty but in the longer term
 even more from those who say things like “The innocent have nothing to fear.”
 - T. Pratchett, Snuff