[petsc-users] MatAssemblyEnd taking too long

Manav Bhatia bhatiamanav at gmail.com
Thu Aug 20 10:08:57 CDT 2020

> On Aug 20, 2020, at 8:31 AM, Stefano Zampini <stefano.zampini at gmail.com> wrote:
> Can you add a MPI_Barrier before
> ierr = MatAssemblyBegin(aij->A,mode);CHKERRQ(ierr);

With a MPI_Barrier before this function call:
—  three of the processes have already hit this barrier, 
—  the other 5 are inside MatStashScatterGetMesg_Private -> MatStashScatterGerMesg_BTS -> MPI_Waitsome(2 processes)/MPI_Waitall(3 processes)

> Also, in order to assess where the issue is, we need to see the values (per rank) of 
> ((Mat_SeqAIJ*)aij->B->data)->nonew
> mat->was_assembled
> aij->donotstash
> mat->nooffprocentries

I am working to get this information. 

> Another question: is this the first matrix assembly of the code?

Yes, this is the first matrix assembly in the code. 

> If you change to pc_none, do you get the same issue?

Yes, with "-pc_type none” the code is stuck at the same spot. 
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