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<p class="MsoNormal"><span style="font-size:11.0pt">An internal acknowledgement message is sent from the receiver to the sender indicating that a particular synchronous send operation was matched.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Ken<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<b><span style="color:black">From: </span></b><span style="color:black">Niyaz Murshed via discuss <discuss@mpich.org><br>
<b>Date: </b>Tuesday, October 8, 2024 at 10:49</span><span style="font-family:"Arial",sans-serif;color:black"> </span><span style="color:black">AM<br>
<b>To: </b>discuss@mpich.org <discuss@mpich.org><br>
<b>Cc: </b>Niyaz Murshed <Niyaz.Murshed@arm.com>, nd <nd@arm.com><br>
<b>Subject: </b>Re: [mpich-discuss] MPI_Send over ibverbs<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:.5in;mso-line-height-alt:.75pt"><span style="font-size:1.0pt;color:white">Thank you for the reply Joachim. ‘MPI_Ssend has the requirement to return after the message was matched at the receiver’ – From the above statement,
how do the sender know that the receiver called a matching receive? I am asking from the point<o:p></o:p></span></p>
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<b><span style="font-family:"Arial",sans-serif;color:black">This Message Is From an External Sender
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">Thank you for the reply Joachim.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">‘MPI_Ssend has the requirement to return after the message was matched at <br>
the receiver’ –</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">From the above statement, how do the sender know that the receiver called a matching receive?</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">I am asking from the point of view of MPI_Send over RDMA.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">In case of RDMA, internally it will call rdma_send which does not know when a matching rdma_recv was called on destination. How do the sender knows when rdma_recv was called?</span><o:p></o:p></p>
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<b><span style="color:black">From: </span></b><span style="color:black">Joachim Jenke via discuss <discuss@mpich.org><br>
<b>Date: </b>Tuesday, October 8, 2024 at 9:42</span><span style="font-family:"Arial",sans-serif;color:black"> </span><span style="color:black">AM<br>
<b>To: </b>discuss@mpich.org <discuss@mpich.org><br>
<b>Cc: </b>Joachim Jenke <jenke@itc.rwth-aachen.de><br>
<b>Subject: </b>Re: [mpich-discuss] MPI_Send over ibverbs</span><o:p></o:p></p>
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<p class="MsoNormal" style="margin-left:.5in"><span style="font-size:11.0pt">Hi,<br>
<br>
none of the MPI send calls has a requirement to return after the message <br>
was received. MPI_Send can return as soon as the caller can write to <br>
buffer without impact to the data being transferred. This might be after <br>
the data is put to the network, or the MPI library copied the data to an <br>
internal buffer.<br>
<br>
MPI_Ssend has the requirement to return after the message was matched at <br>
the receiver, which implies that the matching Receive was called. But it <br>
still does not require that the message was received at this point.<br>
<br>
Best<br>
Joachim<br>
<br>
Am 08.10.24 um 04:55 schrieb Niyaz Murshed via discuss:<br>
> Hi,<br>
> <br>
> Is there a way to check the implementation of MPI_Send?<br>
> <br>
> As I understand there is an implicit barrier which allows MPI_Send to <br>
> return only after the buffer is received by the destination.<br>
> <br>
> How is this communication done? How does the destination notify the <br>
> sender that buffer is received?<br>
> <br>
> How is this implemented when using rocev2 ?<br>
> <br>
> Regards,<br>
> <br>
> Niyaz<br>
> <br>
> <br>
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<br>
-- <br>
Dr. rer. nat. Joachim Jenke<br>
<br>
IT Center<br>
Group: High Performance Computing<br>
Division: Computational Science and Engineering<br>
RWTH Aachen University<br>
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