[petsc-users] Strange Partition in PETSc 3.11 version on some computers

[Mark Adams]

On Tue, Sep 17, 2019 at 12:53 PM Danyang Su <danyang.su at gmail.com> wrote:

> Hi Mark,
>
> Thanks for your follow-up.
>
> The unstructured grid code has been verified and there is no problem in
> the results. The convergence rate is also good. The 3D mesh is not good, it
> is based on the original stratum which I haven't refined, but good for
> initial test as it is relative small and the results obtained from this
> mesh still makes sense.
>
> The 2D meshes are just for testing purpose as I want to reproduce the
> partition problem on a cluster using PETSc3.11.3 and Intel2019.
> Unfortunately, I didn't find problem using this example.
>
> The code has no problem in using different PETSc versions (PETSc V3.4 to
> V3.11)
>
OK, it is the same code. I thought I saw something about your code changing.

Just to be clear, v3.11 never gives you good partitions. It is not just a
problem on this Intel cluster.

The machine, compiler and MPI version should not matter.


> and MPI distribution (MPICH, OpenMPI, IntelMPI), except for one simulation
> case (the mesh I attached) on a cluster with PETSc3.11.3 and Intel2019u4
> due to the very different partition compared to PETSc3.9.3. Yet the
> simulation results are the same except for the efficiency problem because
> the strange partition results into much more communication (ghost nodes).
>
> I am still trying different compiler and mpi with PETSc3.11.3 on that
> cluster to trace the problem. Will get back to you guys when there is
> update.
>

This is very strange. You might want to use 'git bisect'. You set a good
and a bad SHA1 (we can give you this for 3.9 and 3.11 and the exact
commands). The git will go to a version in the middle. You then
reconfigure, remake, rebuild your code, run your test. Git will ask you, as
I recall, if the version is good or bad. Once you get this workflow going
it is not too bad, depending on how hard this loop is of course.


> Thanks,
>
> danyang
>
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