[petsc-users] Using PETSc GPU backend

[Ng, Cho-Kuen]

Barry, Mark and Matt,

Thank you all for the suggestions. I will modify the code so we can pass runtime options.

Cho
________________________________
From: Barry Smith <bsmith at petsc.dev>
Sent: Friday, June 30, 2023 7:01 AM
To: Mark Adams <mfadams at lbl.gov>
Cc: Matthew Knepley <knepley at gmail.com>; Ng, Cho-Kuen <cho at slac.stanford.edu>; petsc-users at mcs.anl.gov <petsc-users at mcs.anl.gov>
Subject: Re: [petsc-users] Using PETSc GPU backend


  Note that options like -mat_type aijcusparse  -vec_type cuda only work if the program is set up to allow runtime swapping of matrix and vector types. If you have a call to MatCreateMPIAIJ() or other specific types then then these options do nothing but because Mark had you use -options_left the program will tell you at the end that it did not use the option so you will know.

On Jun 30, 2023, at 9:30 AM, Mark Adams <mfadams at lbl.gov> wrote:

PetscCall(PetscInitialize(&argc, &argv, NULL, help)); gives us the args and you run:

a.out -mat_type aijcusparse -vec_type cuda -log_view -options_left

Mark

On Fri, Jun 30, 2023 at 6:16 AM Matthew Knepley <knepley at gmail.com<mailto:knepley at gmail.com>> wrote:
On Fri, Jun 30, 2023 at 1:13 AM Ng, Cho-Kuen via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:
Mark,

The application code reads in parameters from an input file, where we can put the PETSc runtime options. Then we pass the options to PetscInitialize(...). Does that sounds right?

PETSc will read command line argument automatically in PetscInitialize() unless you shut it off.

  Thanks,

    Matt

Cho
________________________________
From: Ng, Cho-Kuen <cho at slac.stanford.edu<mailto:cho at slac.stanford.edu>>
Sent: Thursday, June 29, 2023 8:32 PM
To: Mark Adams <mfadams at lbl.gov<mailto:mfadams at lbl.gov>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>>
Subject: Re: [petsc-users] Using PETSc GPU backend

Mark,

Thanks for the information. How do I put the runtime options for the executable, say, a.out, which does not have the provision to append arguments? Do I need to change the C++ main to read in the options?

Cho
________________________________
From: Mark Adams <mfadams at lbl.gov<mailto:mfadams at lbl.gov>>
Sent: Thursday, June 29, 2023 5:55 PM
To: Ng, Cho-Kuen <cho at slac.stanford.edu<mailto:cho at slac.stanford.edu>>
Cc: petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov> <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>>
Subject: Re: [petsc-users] Using PETSc GPU backend

Run with options: -mat_type aijcusparse -vec_type cuda -log_view -options_left

The last column of the performance data (from -log_view) will be the percent flops on the GPU. Check that that is > 0.

The end of the output will list the options that were used and options that were _not_ used (if any). Check that there are no options left.

Mark

On Thu, Jun 29, 2023 at 7:50 PM Ng, Cho-Kuen via petsc-users <petsc-users at mcs.anl.gov<mailto:petsc-users at mcs.anl.gov>> wrote:
I installed PETSc on Perlmutter using "spack install petsc+cuda+zoltan" and used it by "spack load petsc/fwge6pf". Then I compiled the application code (purely CPU code) linking to the petsc package, hoping that I can get performance improvement using the petsc GPU backend. However, the timing was the same using the same number of MPI tasks with and without GPU accelerators. Have I missed something in the process, for example, setting up PETSc options at runtime to use the GPU backend?

Thanks,
Cho


--
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/<http://www.cse.buffalo.edu/~knepley/>

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