[petsc-dev] Additive Schwarz Method + ILU on GPU platforms

[Angus, Justin Ray]

Hi Junchao,

Thanks for the reply.

Does ASM work the same on GPU systems as it does on CPU systems?

From: Junchao Zhang <junchao.zhang at gmail.com>
Date: Monday, April 14, 2025 at 7:35 PM
To: Angus, Justin Ray <angus1 at llnl.gov>
Cc: petsc-dev at mcs.anl.gov <petsc-dev at mcs.anl.gov>, Ghosh, Debojyoti <ghosh5 at llnl.gov>
Subject: Re: [petsc-dev] Additive Schwarz Method + ILU on GPU platforms
Petsc supports ILU0/ICC0 numeric factorization (without reordering) and then triangular solve on GPUs. It is done by calling vendor libraries (ex. cusparse).
We have options -pc_factor_mat_factor_on_host <bool>  -pc_factor_mat_solve_on_host <bool> to force doing the factorization and MatSolve on the host for device matrix types.

You can try to see if it works for your case.

--Junchao Zhang


On Mon, Apr 14, 2025 at 4:39 PM Angus, Justin Ray via petsc-dev <petsc-dev at mcs.anl.gov<mailto:petsc-dev at mcs.anl.gov>> wrote:
Hello,

A project I work on uses GMRES via PETSc. In particular, we have had good successes using the Additive Schwarz Method + ILU preconditioner setup using a CPU-based code. I found online where it is stated that “Parts of most preconditioners run directly on the GPU” (https://urldefense.us/v3/__https://petsc.org/release/faq/__;!!G_uCfscf7eWS!dSU-BKMmIUdQBQGU9qPAHA6zUer96pb6mJWetHYJfQRsaOruqc9Kcm8kBYXWS9GMBF5yITxk6OcMGOpurP_kgQ$ <https://urldefense.us/v3/__https:/petsc.org/release/faq/__;!!G_uCfscf7eWS!bw6qeKcY7MKSvlEgcogdKR7fpjZSOFvka6zfDprUZ_sJHdE-YZmRD6UTqWQW3_uGVBII4P-AG0zaGTLbI67_fQ$>). Is ASM + ILU also available for GPU platforms?

-Justin
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