On 1 Mar 2021, at 6:29 AM, Zhang, Hong <[email protected]> wrote:

Pierre, This is a bug in MatMatMultSymbolic_MPIAIJ_MPIDense() during optimization of block column size of B. Run your code with '-matmatmult_Bbn 1', the infinite loop should not occur.

Thanks Hong, I can confirm this option makes the more complex use case run smoothly as well.

I'll try to figure out a fix tomorrow.

Great. Thanks, Pierre

Hong From: Zhang, Hong <[email protected]> Sent: Sunday, February 28, 2021 11:05 PM To: Pierre Jolivet <[email protected]>; For users of the development version of PETSc <[email protected]>; Zhang, Hong <[email protected]> Subject: Re: [petsc-dev] Infinite loop in A*B

The infinite loop in MatMatMultNumeric_MPIAIJ_MPIDense() for (i=0; i<BN; i+=n) { } is cause by n=contents->workB->cmap->n=0 (line 590 in mpimatmatmult.c) Hong From: petsc-dev <[email protected]> on behalf of Zhang, Hong via petsc-dev <[email protected]> Sent: Sunday, February 28, 2021 10:33 PM To: Pierre Jolivet <[email protected]>; For users of the development version of PETSc <[email protected]> Subject: Re: [petsc-dev] Infinite loop in A*B

I can reproduce the hang with mpiexec -n 2 ./matmatmult

It seems in an infinite loop of calling MatDensePlaceArray() from

#0 MatDensePlaceArray (mat=0xda5c50, array=0xd15e60) at /home/hongsu/soft/petsc/src/mat/impls/dense/mpi/mpidense.c:2047 #1 0x00007fa0d13bf4f7 in MatDenseGetSubMatrix_SeqDense (A=0xcfb2b0, cbegin=0, cend=0, v=0xd90370) at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:2997 #2 0x00007fa0d13c574e in MatDenseGetSubMatrix (A=0xcfb2b0, cbegin=0, cend=0, v=0xd90370) at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:3371 #3 0x00007fa0d13db5ce in MatDenseGetSubMatrix_MPIDense (A=0xca5250, cbegin=0, cend=0, v=0x7ffe87d41de0) at /home/hongsu/soft/petsc/src/mat/impls/dense/mpi/mpidense.c:1835 #4 0x00007fa0d13c574e in MatDenseGetSubMatrix (A=0xca5250, cbegin=0, cend=0, v=0x7ffe87d41de0) at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:3371 #5 0x00007fa0d179c2fa in MatMatMultNumeric_MPIAIJ_MPIDense (A=0xc55490, B=0xca5250, C=0xd282b0) at /home/hongsu/soft/petsc/src/mat/impls/aij/mpi/mpimatmatmult.c:593 #6 0x00007fa0d1181331 in MatProductNumeric_AB (mat=0xd282b0) at /home/hongsu/soft/petsc/src/mat/interface/matproduct.c:567 #7 0x00007fa0d1182c14 in MatProductNumeric (mat=0xd282b0) at /home/hongsu/soft/petsc/src/mat/interface/matproduct.c:679 #8 0x00007fa0d115ef69 in MatProduct_Private (A=0xc55490, B=0xca5250, scall=MAT_INITIAL_MATRIX, fill=-2, ptype=MATPRODUCT_AB, C=0x7ffe87d42018) at /home/hongsu/soft/petsc/src/mat/interface/matrix.c:9405 ---Type <return> to continue, or q <return> to quit--- #9 0x00007fa0d115f274 in MatMatMult (A=0xc55490, B=0xca5250, scall=MAT_INITIAL_MATRIX, fill=-2, C=0x7ffe87d42018) at /home/hongsu/soft/petsc/src/mat/interface/matrix.c:9445 #10 0x000000000040130a in main (argc=2, argv=0x7ffe87d42108) at ex1.c:20

I'll try to figure out what is going on. If anyone has a clue, please help. The above stack comes from 'release' branch. Hong From: petsc-dev <[email protected]> on behalf of Pierre Jolivet <[email protected]> Sent: Sunday, February 28, 2021 4:17 PM To: For users of the development version of PETSc <[email protected]> Subject: [petsc-dev] Infinite loop in A*B

Hello, The following MWE loops indefinitely for MPI_Comm_size in {2; 3}. Nothing fancy, just MatAIJ and MatDense. The problem is either in MatMPIDenseScatter() or MatMatMultSymbolic_MPIAIJ_MPIDense(), I believe, so if someone familiar with those routines can figure out a hot fix, I’m all ears. I could of course switch to a MatMult(), but the same infinite loop happens in another more complex code with A = rows=8, cols=35212 B = rows=35212, cols=9 So I’ll need a fix eventually.

Thanks, Pierre