[petsc-dev] DMFOREST repartitioning in PETSc

[Matthew Knepley]

On Thu, Mar 22, 2018 at 11:45 AM, Saurabh Chawdhary <schawdhary at anl.gov>
wrote:

> Thank you Tobin. I was actually more interested in repartitioning after
> the mesh has been dynamically changed (say, after refinement in certain
> portions of mesh).
>

That kinds of repartitioning in p4est is handled by just splitting the
Morton order into equal pieces, not by a graph partitioner.

   Matt


> On 03/22/2018 07:10 AM, Tobin Isaac wrote:
>
>>
>> On March 21, 2018 11:26:35 AM MDT, Saurabh Chawdhary <schawdhary at anl.gov>
>> wrote:
>>
>>> Hello team,
>>>
>>> I haven't used petsc since DMFOREST was released but I have a question
>>> regarding repartitioning of DMFOREST mesh. How is the repartitioning of
>>>
>>> mesh over processors done after some mesh refinement is carried out? Is
>>>
>>> it done by calling a p4est function or partitioning is done in PETSc?
>>>
>>> I was using p4est (natively) a couple of years ago and I remember that
>>> when I tried to partition the grid I could only use the serial METIS
>>> and
>>> not the parMETIS with p4est (using a native function
>>> /p4est_connectivity_reorder/). So what I want to know is whether
>>> DMFOREST repartitioning is done in parallel or in serial?
>>>
>> You can use the following workflow:
>>
>> - Create/read-only an unstructured hexahedral mesh as a DMPlex
>> - Use ParMETIS to repartition that: there is a ParMETIS implementation of
>> PetscPartitioner, which creates index sets and communication patterns for
>> DMPlexDistribute.
>> - Convert the DMPlex to DMP4est or DMP8est.
>>
>> This does not avoid the fundamental limitations of p4est: the distributed
>> mesh will be redundantly serialized behind-the-scenes, and the coarse-mesh
>> ordering derived from ParMETIS will be static for the life of the forest
>> mesh.
>>
> I am not sure I understand how the distributed mesh is redundantly
> serialized in p4est. Do you mean that the partitioning is done serially?
>
>>
>>
>>> Thank you.
>>>
>>> Saurabh
>>>
>>
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
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https://www.cse.buffalo.edu/~knepley/ <http://www.caam.rice.edu/~mk51/>
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