[petsc-users] Load imbalance in DMSwarm & DMDA simulations

[Mark Adams]

This tool works at the Mat level so it does not matter, but you need to
work at the DM level anyway.

I don't know of DM tools for this. Let Matt chime in.


On Tue, Mar 17, 2026 at 7:54 AM Miguel Molinos <m.molinos at upm.es> wrote:

> Thank you Mark. Indeed my question was oriented towards the tools PETSc
> can offer to address this problem. Currently I’m using DMDA, perhaps DMPlex
> is more suited?
>
> Thanks,
> Miguel
>
> On 17 Mar 2026, at 12:17, Mark Adams <mfadams at lbl.gov> wrote:
>
> Hi Miguel,
>
> This is a common problem. To my knowledge you need to deal with it on your
> side, but PETSc does have tools to help.
> I would look in the literature to get ideas and acclimate yourself to the
> problem.
>
> The tool that PETSc has is you can repartition your mesh. Create a dual
> graph (any petsc examples?) put weights on the "vertice" (now elements, use
> particle count) and repartition.
> I am not sure of the best way to proceed from here ... you could create a
> new DMSwarm with this new "cell" DM and add particles from the old to the
> new, delete the old, call DMMigrate on the new DMSwarm and that will do the
> moving that we want.
>
> Others will probably be able to add to this.
>
> Thanks,
> Mark
>
>
> On Tue, Mar 17, 2026 at 4:49 AM Miguel Molinos <m.molinos at upm.es> wrote:
>
>>
>> Dear all,
>>
>> I am currently running a PIC-like implementation based on DMSwarm and
>> DMDA. In my setup, a particle (DMSwarm) discretization represents, for
>> example, a sphere placed at the center of a box-shaped domain discretized
>> with a regular mesh (DMDA).
>>
>> The implementation uses both MPI and OpenMP to accelerate the
>> computations. The domain decomposition of the sphere follows a PIC-like
>> approach: each particle is assigned to a rank based on the mesh element it
>> belongs to, and thus inherits the rank that “owns” that element. This is
>> essentially the same strategy used in one of the PETSc examples.
>>
>> However, I have observed that, for certain configurations, some ranks end
>> up with very few or even no particles, which leads to load imbalance.
>>
>> Has anyone experienced a similar issue?
>>
>> Thanks,
>> Miguel
>>
>
>
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