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@gmail.com>
Date: Monday, April 14, 2025 at 7:35 PM
To: Angus, Justin Ray <angus1@llnl.gov>
Cc: petsc-dev@mcs.anl.gov <petsc-dev@mcs.anl.gov>, Ghosh, Debojyoti <ghosh5@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@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://petsc.org/release/faq/). Is ASM + ILU also available for GPU platforms?

-Justin