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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Hi Sunwoo,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">In general I think that you should be aware that the asynchronous operations in MPI are there to take advantage of RDMA capable networks. With most simple TCP/IP based networks, the interfaces
are passive and thus data movement between peers can only be made by actively calling MPI functionality. You’ve already noticed that messages will be advanced by calling MPI_Wait. The general point to be made is that on non-RDMA capable networks, an independent
thread or your main program can call MPI_Wait or other MPI calls such as MPI_Test to force the library to actively move data that has been queued by an asynchronous operation. In summary, the answer to your overall question is at best: a qualified yes (depending
on the network capabilities of your cluster or if you employ multithreading). <o:p>
</o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">I hope that explanation helps…<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri">Richard A. Warren (HDFgroup)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:Calibri"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-family:Calibri;color:black">From: </span>
</b><span style="font-family:Calibri;color:black">Sunwoo Lee <sunwoolee1.2014@u.northwestern.edu><br>
<b>Reply-To: </b>"discuss@mpich.org" <discuss@mpich.org><br>
<b>Date: </b>Tuesday, February 21, 2017 at 12:19 PM<br>
<b>To: </b>"discuss@mpich.org" <discuss@mpich.org><br>
<b>Subject: </b>[mpich-discuss] Does Asynchronous Allgather work in background without any effects on computing cores?<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"><span style="font-size:9.5pt">Hi,</span> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">I would like to implement a software that communication and computation are performed simultaneously. That is, while communication for the current data is done, the next data is computed overlapping with the
communication.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">I expected asynchronous MPI such as Iallgather() would make the communication and computation overlapped. But it seems like the communication is not started until I call MPI_Wait(). <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">With a simple toy application, I compared the two cases. MPI_IAllgather + MPI_Wait() versus MPI_Allgather. The issue is that MPI_Wait() takes almost same time with MPI_Allgather. I can guess the communication
is just started when I call MPI_Wait. <o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">My question is, could asynchronous MPI functions work background so that computing cores do other works while the communication is performed?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Thank you.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Best,<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:9.5pt">Sunwoo Lee<o:p></o:p></span></p>
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