[petsc-users] [MPI GPU Aware] KSP_DIVERGED

[Satish Balay]

And/Or - try latest OpenMPI [or MPICH] and see if that makes a difference.

--download-mpich or --download-openmpi with latest petsc should build gpu-aware-mpi

Satish

On Mon, 16 Sep 2024, Junchao Zhang wrote:

> Could you try petsc/main to see if the problem persists?
> 
> --Junchao Zhang
> 
> 
> On Mon, Sep 16, 2024 at 10:51 AM LEDAC Pierre <Pierre.LEDAC at cea.fr> wrote:
> 
> > Hi all,
> >
> >
> > We are using PETSc 3.20 in our code and running succesfully several
> > solvers on Nvidia GPU with OpenMPI library which are not GPU aware (so I
> > need to add the flag -use_gpu_aware_mpi 0).
> >
> >
> > But now, when using OpenMPI GPU Aware library (OpenMPI 4.0.5 ou 4.1.5 from
> > NVHPC), some parallel calculations failed with *KSP_DIVERGED_ITS* or
> > *KSP_DIVERGED_DTOL*
> >
> > with several configurations. It may run wells on a small test case with
> > (matrix is symmetric):
> >
> >
> > *-ksp_type cg -pc_type gamg -pc_gamg_type classical*
> >
> >
> > But suddenly with a number of devices for instance bigger than 4 or 8, it
> > may fail.
> >
> >
> > If I switch to another solver (BiCGstab), it may converge:
> >
> >
> > *-ksp_type bcgs -pc_type gamg -pc_gamg_type classical*
> >
> >
> > The more sensitive cases where it diverges are the following:
> >
> >
> > *-ksp_type cg -pc_type hypre -pc_hypre_type boomeramg *
> >
> > *-ksp_type cg -pc_type gamg  -pc_gamg_type classical*
> >
> >
> > And the *bcgs* turnaroud doesn't work each time...
> >
> >
> > It seems to work without problem with aggregation (at least 128 GPUs on my
> > simulation):
> >
> > *-ksp_type cg -pc_type gamg -pc_gamg_type agg*
> >
> >
> > So I guess there is a weird thing happening in my code during the solve in
> > PETSc with MPI GPU Aware, as all the previous configurations works with non
> > GPU aware MPI.
> >
> >
> > Here is the -ksp_view log during one fail with the first configuration:
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> > *KSP Object: () 8 MPI processes   type: cg   maximum iterations=10000,
> > nonzero initial guess   tolerances:  relative=0., absolute=0.0001,
> > divergence=10000.   left preconditioning   using UNPRECONDITIONED norm type
> > for convergence test PC Object: () 8 MPI processes   type: hypre     HYPRE
> > BoomerAMG preconditioning       Cycle type V       Maximum number of levels
> > 25       Maximum number of iterations PER hypre call 1       Convergence
> > tolerance PER hypre call 0.       Threshold for strong coupling 0.7
> > Interpolation truncation factor 0.       Interpolation: max elements per
> > row 0       Number of levels of aggressive coarsening 0       Number of
> > paths for aggressive coarsening 1       Maximum row sums 0.9       Sweeps
> > down         1       Sweeps up           1       Sweeps on coarse    1
> >       Relax down          l1scaled-Jacobi       Relax up
> > l1scaled-Jacobi       Relax on coarse     Gaussian-elimination       Relax
> > weight  (all)      1.       Outer relax weight (all) 1.       Maximum size
> > of coarsest grid 9       Minimum size of coarsest grid 1       Not using
> > CF-relaxation       Not using more complex smoothers.       Measure
> > type        local       Coarsen type        PMIS       Interpolation type
> > ext+i       SpGEMM type         cusparse   linear system matrix = precond
> > matrix:   Mat Object: () 8 MPI processes     type: mpiaijcusparse
> > rows=64000, cols=64000     total: nonzeros=311040, allocated
> > nonzeros=311040     total number of mallocs used during MatSetValues
> > calls=0       not using I-node (on process 0) routines*
> >
> >
> > I didn't succeed for the moment creating a reproducer with ex.c examples...
> >
> >
> > Did you see this kind of behaviour before?
> >
> > Should I update my PETSc version ?
> >
> >
> > Thanks for any advice,
> >
> >
> > Pierre LEDAC
> > Commissariat à l’énergie atomique et aux énergies alternatives
> > Centre de SACLAY
> > DES/ISAS/DM2S/SGLS/LCAN
> > Bâtiment 451 – point courrier n°43
> > F-91191 Gif-sur-Yvette
> > +33 1 69 08 04 03
> > +33 6 83 42 05 79
> >
>