[petsc-users] [MPI][GPU]

[LEDAC Pierre]

Barry,


It solved the unrecognized option but still exchanging MPI messages through the host.


I switch to a simpler test case without reading a matrix (src/ksp/ksp/tutorials/ex46.c) but get the same behaviour.


In the Nsys profile for ex46, the MPI synchronizations occurs during PCApply so now I am wondering if the issue is related to the fact than Hypre is not configured/enabled with MPI GPU-Aware in the PETSc build.

I will give a try with --enable-gpu-aware-mpi passed to Hypre.


Do you know an example in PETSc which specifically bench with/without Cuda-Aware enabled for MPI ?


[cid:93d886d4-28ec-4b73-b602-3a559fffd435]


Pierre LEDAC
Commissariat à l’énergie atomique et aux énergies alternatives
Centre de SACLAY
DES/ISAS/DM2S/SGLS/LCAN
Bâtiment 451 – point courrier n°41
F-91191 Gif-sur-Yvette
+33 1 69 08 04 03
+33 6 83 42 05 79
________________________________
De : Barry Smith <bsmith at petsc.dev>
Envoyé : dimanche 31 août 2025 16:33:38
À : LEDAC Pierre
Cc : petsc-users at mcs.anl.gov
Objet : Re: [petsc-users] [MPI][GPU]


  Ahh, that ex10.c is missing a VecSetFromOptions() call before the VecLoad() and friends. In contrast, the matrix has a MatSetFromOptions(). Can you try adding it to ex10.c and see if that resolves the problem with ex10.c (and may be a path forward for your code)?

  Barry


On Aug 31, 2025, at 4:32 AM, LEDAC Pierre <Pierre.LEDAC at cea.fr> wrote:

Yes, but was surprised it was not used, so I removed it (same for -vec_type mpicuda)

mpirun -np 2 ./ex10 2 -f Matrix_3133717_rows_1_cpus.petsc -ksp_view -log_view -ksp_monitor -ksp_type cg -pc_type hypre -pc_hypre_type boomeramg -pc_hypre_boomeramg_strong_threshold 0.7 -mat_type aijcusparse -vec_type cuda
...

WARNING! There are options you set that were not used!
WARNING! could be spelling mistake, etc!
There is one unused database option. It is:
Option left: name:-vec_type value: cuda source: command lin

Pierre LEDAC
Commissariat à l’énergie atomique et aux énergies alternatives
Centre de SACLAY
DES/ISAS/DM2S/SGLS/LCAN
Bâtiment 451 – point courrier n°41
F-91191 Gif-sur-Yvette
+33 1 69 08 04 03
+33 6 83 42 05 79
________________________________
De : Barry Smith <bsmith at petsc.dev<mailto:bsmith at petsc.dev>>
Envoyé : samedi 30 août 2025 21:47:07
À : LEDAC Pierre
Cc : petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>
Objet : Re: [petsc-users] [MPI][GPU]


Did you try the additional option -vec_type cuda with ex10.c ?



On Aug 30, 2025, at 1:16 PM, LEDAC Pierre <Pierre.LEDAC at cea.fr<mailto:Pierre.LEDAC at cea.fr>> wrote:

Hello,

My code is built with PETSc 3.23+OpenMPI 4.1.6 (Cuda support enabled) and profling indicates that MPI communications are done between GPUs in all the code except PETSc part where D2H transfers occur.

I reproduced the PETSc issue with the example under src/ksp/ksp/tutorials/ex10 on 2 MPI ranks. See output in ex10.log

Also below the Nsys system profiling on ex10 with D2H and H2D copies before/after MPI calls.

Thanks for your help,

<pastedImage.png>


Pierre LEDAC
Commissariat à l’énergie atomique et aux énergies alternatives
Centre de SACLAY
DES/ISAS/DM2S/SGLS/LCAN
Bâtiment 451 – point courrier n°41
F-91191 Gif-sur-Yvette
+33 1 69 08 04 03
+33 6 83 42 05 79
<ex10.log>

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