[petsc-users] Kokkos Interface for PETSc

Thu Feb 17 17:33:17 CST 2022

Hi Philip,

Sorry to be a bit late in my reply. Jed has explained the gist of what's 
involved with using the Kokkos/Kokkos-kernels back-end for the PETSc 
solves, though, depending on exactly how Xolotl creates its vectors, 
there may be a bit of work required to ensure that the command-line 
options specifying the matrix and GPU types get applied to the right 
objects, and that non-GPU types are not being hardcoded somewhere (by a 
call like "DMSetMatType(dm,MATAIJ)").

In addition to looking at the -log_view output, since Xolotl uses TS you 
can specify "-ts_view" and look at the output that describes the solver 
hierarchy that Xolotl sets up. If matrix types are being set correctly, 
you'll see things like

       Mat Object: 1 MPI processes
         type: seqaijkokkos

(I note that I've also sent a related message about getting Xolotl 
working with Kokkos back-ends on Summit to you, Sophie, and Phil in 
reply to old thread about this.)

Were you also asking about how to use Kokkos for PETSc matrix assembly, 
or is that a question for later?

Cheers,
Richard

On 2/15/22 09:07, Satish Balay via petsc-users wrote:
> Also - perhaps the following info might be useful
>
> Satish
>
> ----
>
> balay at sb /home/balay/petsc (main=)
> $ git grep -l download-kokkos-kernels config/examples
> config/examples/arch-ci-freebsd-cxx-cmplx-pkgs-dbg.py
> config/examples/arch-ci-linux-cuda-double.py
> config/examples/arch-ci-linux-gcc-ifc-cmplx.py
> config/examples/arch-ci-linux-hip-double.py
> config/examples/arch-ci-linux-pkgs-dbg-ftn-interfaces.py
> config/examples/arch-ci-linux-pkgs-valgrind.py
> config/examples/arch-ci-osx-cxx-pkgs-opt.py
> config/examples/arch-nvhpc.py
> config/examples/arch-olcf-crusher.py
> config/examples/arch-olcf-spock.py
> balay at sb /home/balay/petsc (main=)
> $ git grep -l "requires:.*kokkos_kernels"
> src/ksp/ksp/tests/ex3.c
> src/ksp/ksp/tests/ex43.c
> src/ksp/ksp/tests/ex60.c
> src/ksp/ksp/tutorials/ex7.c
> src/mat/tests/ex123.c
> src/mat/tests/ex132.c
> src/mat/tests/ex2.c
> src/mat/tests/ex250.c
> src/mat/tests/ex251.c
> src/mat/tests/ex252.c
> src/mat/tests/ex254.c
> src/mat/tests/ex5.c
> src/mat/tests/ex62.c
> src/mat/tutorials/ex5k.kokkos.cxx
> src/snes/tests/ex13.c
> src/snes/tutorials/ex13.c
> src/snes/tutorials/ex3k.kokkos.cxx
> src/snes/tutorials/ex56.c
> src/ts/utils/dmplexlandau/tutorials/ex1.c
> src/ts/utils/dmplexlandau/tutorials/ex1f90.F90
> src/ts/utils/dmplexlandau/tutorials/ex2.c
> src/vec/vec/tests/ex21.c
> src/vec/vec/tests/ex22.c
> src/vec/vec/tests/ex23.c
> src/vec/vec/tests/ex28.c
> src/vec/vec/tests/ex34.c
> src/vec/vec/tests/ex37.c
> src/vec/vec/tests/ex38.c
> src/vec/vec/tests/ex4.c
> src/vec/vec/tests/ex43.c
> src/vec/vec/tests/ex60.c
> src/vec/vec/tutorials/ex1.c
> balay at sb /home/balay/petsc (main=)
> $
>
> On Tue, 15 Feb 2022, Satish Balay via petsc-users wrote:
>
>> Also - best to use petsc repo - 'main' branch.
>>
>> And for install on crusher - check config/examples/arch-olcf-crusher.py
>>
>> Satish
>>
>> On Tue, 15 Feb 2022, Jed Brown wrote:
>>
>>> We need to make these docs more explicit, but the short answer is configure with --download-kokkos --download-kokkos-kernels and run almost any example with -dm_mat_type aijkokkos -dm_vec_type kokkos. If you run with -log_view, you should see that all the flops take place on the device and there are few host->device transfers. Message packing is done on the device and it'll use GPU-aware MPI. There are a few examples of residual evaluation and matrix assembly on the device using Kokkos. You can also see libCEED examples for assembly on the device into Kokkos matrices and vectors without touching host memory.
>>>
>>> "Fackler, Philip via petsc-users"<petsc-users at mcs.anl.gov>  writes:
>>>
>>>> We're intending to transitioning the Xolotl interfaces with PETSc.
>>>>
>>>> I am hoping someone (can) point us to some documentation (and examples) for using PETSc's Kokkos-based interface. If this does not yet exist, then perhaps some slides (like the ones Richard Mills showed at the NE-SciDAC all-hands meeting) showing some examples could get us started.
>>>>
>>>> Thanks for any help that can be provided,
>>>>
>>>> Philip Fackler
>>>> Research Software Engineer, Application Engineering Group
>>>> Advanced Computing Systems Research Section
>>>> Computer Science and Mathematics Division
>>>> Oak Ridge National Laboratory
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