On Wed, 26 Nov, 2014 at 7:50 AM, Johan Hake <[email protected]> wrote:
On Wed, Nov 26, 2014 at 8:34 AM, Garth N. Wells <[email protected]>
wrote:
On Tue, 25 Nov, 2014 at 9:48 PM, Johan Hake <[email protected]>
wrote:
Hello!
I just pushed some fixes to the jit interface of DOLFIN. Now one
can jit on different mpi groups.
Nice.
Previously jiting was only done on rank 1 of the mpi_comm_world.
Now it is done on rank 1 of any passed group communicator.
Do you mean rank 0?
Yes, of course.
There is no demo atm showing this but a test has been added:
test/unit/python/jit/test_jit_with_mpi_groups.py
Here an expression, a subdomain, and a form is constructed on
different ranks using group. It is somewhat tedious as one need to
initialize PETSc with the same group, otherwise PETSc will deadlock
during initialization (the moment a PETSc la object is constructed).
This is ok. It's arguably a design flaw that we don't make the user
handle MPI initialisation manually.
Sure, it is just somewhat tedious. You cannot start your typical
script with importing dolfin.
The procedure in Python for this is:
1) Construct mpi groups using mpi4py
2) Initalize petscy4py using the groups
3) Wrap groups to petsc4py comm (dolfin only support petsc4py not
mpi4py)
4) import dolfin
5) Do group specific stuff:
a) Function and forms no change needed as communicator
is passed via mesh
b) domain = CompiledSubDomain("...", mpi_comm=group_comm)
c) e = Expression("...", mpi_comm=group_comm)
It's not so clear whether passing the communicator means that the
Expression is only defined/available on group_comm, or if group_comm
is simply to control who does the JIT. Could you clarify this?
My knowledge is not that good in MPI. I have only tried to access
(and construct) the Expression on ranks included in that group. Also
when I tried construct one using a group communicator on a rank that
is not included in the group, I got an when calling MPI_size on it.
There is probably a perfectly reasonable explaination to this.
Could you clarify what goes on behind-the-scenes with the communicator?
Is it only used in a call to get the process rank? What do the ranks
other than zero do?
Garth
Please try it out and report any sharp edges. A demo would also be
fun to include :)
We could run tests on different communicators to speed them up on
machines with high core counts!
True!
Johan
Garth
Johan
_______________________________________________
fenics mailing list
[email protected]
http://fenicsproject.org/mailman/listinfo/fenics
