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<p class="MsoNormal"><span style="font-size:12.0pt">Hi Shuwei,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">The MPICH library does not implement a hard limit on the number of ranks. That being said, the rank is stored as a 32bit integer, therefore subject to the limit of MAX_INT. In practice, it is more likely that
the library will run out-of-memory before hitting that limit.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">MPICH is optimized for large scale use cases than contains hundreds of thousands processes, so it should be fine for your use cases.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">Yanfei Guo<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-family:"Courier New"">Assistant Computer Scientist<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-family:"Courier New"">MCS, ANL</span><span style="font-size:12.0pt"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Shuwei Zhao via discuss <discuss@mpich.org><br>
<b>Reply-To: </b>"discuss@mpich.org" <discuss@mpich.org><br>
<b>Date: </b>Monday, October 29, 2018 at 3:43 PM<br>
<b>To: </b>"discuss@mpich.org" <discuss@mpich.org><br>
<b>Cc: </b>Shuwei Zhao <shuweizhao1991@gmail.com><br>
<b>Subject: </b>[mpich-discuss] Maximum number of processes in compute farm<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Hi, all <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I have several questions about parallel scale of mpich: <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Is there a hard limit on the number of processes that mpich can start in a compute farm? <o:p></o:p></p>
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<p class="MsoNormal">As the number of process going up , for a large-scale(1000-10000) loose-communication application(the communication overhead is minimal compared to the runtime), is it possible that the performance of the mpich will go down because the
message passing will take longer time? <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thank you very much, <o:p></o:p></p>
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<p class="MsoNormal">Shuwei<o:p></o:p></p>
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