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Dear PETSc’s developers, I hope this email finds you well. I am currently working on a project using PETSc and have encountered a performance issue with the KSPSolve function. Specifically, I have noticed that the time taken by KSPSolve is
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">Dear
</span><span lang="EN-US" style="color:black;mso-ligatures:none">PETSc’s developers</span><span style="color:black;mso-ligatures:none">,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">I hope this email finds you well.<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">I am currently working on a project using PETSc and have encountered a performance issue with the </span><span style="font-size:10.0pt;font-family:"Courier New";color:black;mso-ligatures:none">KSPSolve</span><span style="color:black;mso-ligatures:none"> function.
Specifically, <b>I have noticed that the time taken by </b></span><b><span style="font-size:10.0pt;font-family:"Courier New";color:black;mso-ligatures:none">KSPSolve</span></b><b><span style="color:black;mso-ligatures:none"> is
</span></b><b><span lang="EN-US" style="color:black;mso-ligatures:none">almost two times
</span></b><b><span style="color:black;mso-ligatures:none">greater than the CPU time for matrix-vector product multiplied by the number of iteration steps</span></b><span style="color:black;mso-ligatures:none">.</span><span style="color:black;mso-ligatures:none">
<span lang="EN-US">I use C++ chrono to record CPU time.<o:p></o:p></span></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">For context, I am using a shell system matrix</span><span lang="EN-US" style="color:black;mso-ligatures:none"> A</span><span style="color:black;mso-ligatures:none">.
Despite my efforts to </span><span lang="EN-US" style="color:black;mso-ligatures:none">parallelize</span><span style="color:black;mso-ligatures:none"> the matrix-vector product</span><span lang="EN-US" style="color:black;mso-ligatures:none"> (Ax)</span><span style="color:black;mso-ligatures:none">,
the overall solve time remains higher</span><span lang="EN-US" style="color:black;mso-ligatures:none"> than the matrix vector product per iteration indicates when multiple threads were used</span><span style="color:black;mso-ligatures:none">. Here are a few
details of my setup:<o:p></o:p></span></p>
<ul type="disc">
<li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<b><span style="mso-ligatures:none">Matrix Type</span></b><span style="mso-ligatures:none">: Shell system matrix<o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<b><span style="mso-ligatures:none">Preconditioner</span></b><span style="mso-ligatures:none">:
</span><span lang="EN-US" style="mso-ligatures:none">Shell PC</span><span style="mso-ligatures:none"><o:p></o:p></span></li><li class="MsoNormal" style="color:black;mso-margin-top-alt:auto;mso-margin-bottom-alt:auto;mso-list:l0 level1 lfo1">
<b><span style="mso-ligatures:none">Parallel Environment</span></b><span style="mso-ligatures:none">:
</span><span lang="EN-US" style="mso-ligatures:none">Using Intel MKL as PETSc’s BLAS/LAPACK library, multithreading is enabled
</span><span style="mso-ligatures:none"><o:p></o:p></span></li></ul>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="color:black;mso-ligatures:none">I have considered several potential reasons, such as preconditioner setup, additional solver operations, and the inherent
overhead of using a shell system matrix. <b>However, since KSPSolve is a high-level API, I have been unable to pinpoint the exact cause of the increased solve time.<o:p></o:p></b></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="color:black;mso-ligatures:none">Have you observed the same issue?
</span><span style="color:black;mso-ligatures:none">Could you</span><span lang="EN-US" style="color:black;mso-ligatures:none"> please</span><span lang="EN-US" style="color:black;mso-ligatures:none">
</span><span style="color:black;mso-ligatures:none">provide some </span><span lang="EN-US" style="color:black;mso-ligatures:none">experience</span><span style="color:black;mso-ligatures:none"> on how to diagnose and address this performance discrepancy? Any
insights or recommendations you could offer would be greatly appreciated.<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">Thank you for your time and assistance.<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span style="color:black;mso-ligatures:none">Best</span><span lang="EN-US" style="color:black;mso-ligatures:none"> regards,<o:p></o:p></span></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><span lang="EN-US" style="color:black;mso-ligatures:none">Yongzhong<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none">-----------------------------------------------------------<o:p></o:p></span></p>
<p class="MsoNormal"><b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none">Yongzhong Li</span></b><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none">PhD student | Electromagnetics Group<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none">Department of Electrical & Computer Engineering<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none">University of Toronto<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US" style="font-size:11.0pt;font-family:"Calibri",sans-serif;mso-ligatures:none"><a href="https://urldefense.us/v3/__http://www.modelics.org__;!!G_uCfscf7eWS!YME6NPPibCKcgA6BRrCcOZBp90jG3xcObexgXGxsVV6i12v_JAnZlhZNJ1SQdikKzM6jBmFVU2Tqrhfjag9YiyROKq6IsdoQ8Lw$"><span style="color:#0563C1">http://www.modelics.org</span></a><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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