<div dir="ltr"><div>Hi, Justin,</div><div> I don't know ASM well enough. I just browsed its code. It seems it has a lot of matrix partitioning and indexing operations, which definitely are not done on GPUs currently.</div><div> But you could still try that, as petsc will copy data from the device to the host as needed to perform host-only operations. You can profile with -log_vew -log_view_gpu_time so that we can see how expensive these operations are.</div><div><br></div><div> Barry should know more about ASM. </div><div><br></div><div>--Junchao Zhang</div><br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Tue, Apr 15, 2025 at 10:43 AM Angus, Justin Ray <<a href="mailto:angus1@llnl.gov">angus1@llnl.gov</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-4952117823530399171">
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<p class="MsoNormal"><span style="font-size:11pt">Hi Junchao,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt">Thanks for the reply.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt">Does ASM work the same on GPU systems as it does on CPU systems?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt"><u></u> <u></u></span></p>
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<p class="MsoNormal" style="margin-bottom:12pt"><b><span style="font-size:12pt;color:black">From:
</span></b><span style="font-size:12pt;color:black">Junchao Zhang <<a href="mailto:junchao.zhang@gmail.com" target="_blank">junchao.zhang@gmail.com</a>><br>
<b>Date: </b>Monday, April 14, 2025 at 7:35</span><span style="font-size:12pt;font-family:Arial,sans-serif;color:black"> </span><span style="font-size:12pt;color:black">PM<br>
<b>To: </b>Angus, Justin Ray <<a href="mailto:angus1@llnl.gov" target="_blank">angus1@llnl.gov</a>><br>
<b>Cc: </b><a href="mailto:petsc-dev@mcs.anl.gov" target="_blank">petsc-dev@mcs.anl.gov</a> <<a href="mailto:petsc-dev@mcs.anl.gov" target="_blank">petsc-dev@mcs.anl.gov</a>>, Ghosh, Debojyoti <<a href="mailto:ghosh5@llnl.gov" target="_blank">ghosh5@llnl.gov</a>><br>
<b>Subject: </b>Re: [petsc-dev] Additive Schwarz Method + ILU on GPU platforms<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt">Petsc supports ILU0/ICC0 numeric factorization (without reordering) and then triangular solve on GPUs. It is done by calling vendor libraries (ex. cusparse).<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt">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.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt">You can try to see if it works for your case.<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt">--Junchao Zhang<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt"><u></u> <u></u></span></p>
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<p class="MsoNormal"><span style="font-size:12pt">On Mon, Apr 14, 2025 at 4:39</span><span style="font-size:12pt;font-family:Arial,sans-serif"> </span><span style="font-size:12pt">PM Angus, Justin Ray via petsc-dev <<a href="mailto:petsc-dev@mcs.anl.gov" target="_blank">petsc-dev@mcs.anl.gov</a>>
wrote:<u></u><u></u></span></p>
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<p class="MsoNormal"><span style="font-size:11pt">Hello,</span><span style="font-size:12pt"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt"> </span><span style="font-size:12pt"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt">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” (<a href="https://urldefense.us/v3/__https:/petsc.org/release/faq/__;!!G_uCfscf7eWS!bw6qeKcY7MKSvlEgcogdKR7fpjZSOFvka6zfDprUZ_sJHdE-YZmRD6UTqWQW3_uGVBII4P-AG0zaGTLbI67_fQ$" target="_blank">https://petsc.org/release/faq/</a>).
Is ASM + ILU also available for GPU platforms?</span><span style="font-size:12pt"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt"> </span><span style="font-size:12pt"><u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt">-Justin</span><span style="font-size:12pt"><u></u><u></u></span></p>
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