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<p class="MsoNormal">Hi Min, <o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Following up, we have a pull request, <a href="https://github.com/pmodels/mpich/pull/5201">
https://github.com/pmodels/mpich/pull/5201</a>, should add the configure option --with-ch4-ucx-rankbits=<N> . You can configure the rankbits for ch4:ucx to between 16 and 32. We are expected to merge this PR soon.<o:p></o:p></p>
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<p class="MsoNormal">-- <br>
Hui Zhou<o:p></o:p></p>
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<b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Zhou, Hui <zhouh@anl.gov><br>
<b>Date: </b>Thursday, April 8, 2021 at 10:18 AM<br>
<b>To: </b>discuss@mpich.org <discuss@mpich.org><br>
<b>Cc: </b>M Xie <xmxmxie@gmail.com><br>
<b>Subject: </b>Re: [mpich-discuss] Supporting > 64K ranks in CH4/UCX netmod<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in">Hi Min, <o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"> <o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">I think we can do something about it. We’ll follow-up when we have updates.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in">-- <br>
Hui Zhou<o:p></o:p></p>
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<b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">M Xie via discuss <discuss@mpich.org><br>
<b>Date: </b>Thursday, April 8, 2021 at 12:30 AM<br>
<b>To: </b>discuss@mpich.org <discuss@mpich.org><br>
<b>Cc: </b>M Xie <xmxmxie@gmail.com><br>
<b>Subject: </b>[mpich-discuss] Supporting > 64K ranks in CH4/UCX netmod</span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">Hi,<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">I am using MPICH on CH4/UCX netmod, the version is mpich-3.4.1.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">I noticed that there is a configure parameter "--with-ch4-rank-bits" which can set the value of CH4_RANK_BITS, but seems CH4_RANK_BITS is not used in the code.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">And I also find in the netmod/ucx/ucx_impl.h, _UCX_init_tag()/_UCX_recv_tag() use only 16 bits to set MPI rank in the ucp_tag, but this cannot differentiate correct ucp_tag when MPI ranks exceed 64K.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">In Open MPI, 20 bits is used in pml/ucx module to set rank in ucp_tag, 20 bits for context, 24 bits for MPI tag, thus the maximum ranks in Open MPI can be 1M.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">Is there any plan to support > 64K ranks in MPICH/CH4/UCX?<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">Thanks.<o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in"> <o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:1.0in">Min<o:p></o:p></p>
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