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<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>All,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>During the DAT con-call today it was suggested that I draft the
application requirements for immediate data. Here is my first cut; fire away!<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>“Applications need an optimized mechanism to notify the receiving
end that RDMA write data has completed beyond the two operation method currently
used (RDMA write followed by message send). This new RDMA write feature will support
4-bytes of inline data that will be sent immediately after the RDMA write
operation is complete. It should avoid any latency penalties normally associated
with a two operation method. The initiating side must expose a 4-byte immediate
data parameter for the application to set the inline data. The receiving side
must provide a mechanism to accept the 4-byte immediate data. On the receiving
side, the write with immediate completion notification is indicated through a receive
completion. It is the responsibility of the provider to identify to the
application 4-byte immediate data from a normal 4-byte send message. The inline
byte ordering is application specific.”<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Hopefully, this will help us come to a consensus on the proper
interface and delivery mechanism for immediate data. <font color=navy><span
style='color:navy'><o:p></o:p></span></font></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Thanks,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>-arlin</span></font><font size=2 color=navy face=Arial><span
style='font-size:10.0pt;font-family:Arial;color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Hefty, Sean <br>
<b><span style='font-weight:bold'>Sent:</span></b> Thursday, February 02, 2006
3:54 PM<br>
<b><span style='font-weight:bold'>To:</span></b> Davis, Arlin R; <st1:PersonName
w:st="on">dat-discussions@yahoogroups.com</st1:PersonName><br>
<b><span style='font-weight:bold'>Cc:</span></b> Lentini, James;
openib-general@openib.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> RE: [dat-discussions] RE:
[openib-general] RE: [RFC] DAT 2.0immediate data proposal</span></font><o:p></o:p></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div style='border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt'>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Here is an updated immediate data proposal
based on the latest discussions. I am working on a patch.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>I don’t see any app using this unless immediate data
is supported, and the data shows up in a completion.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>You have variables to indicate support, the number of work
requests immediate consumes, and how the data is reported. What app is
going to use this? If writes are not supported, then the app will already
have to deal with doing a write followed by their own send. As a further
complication, reserving the first 4 bytes of any receive buffer for immediate
data is only going to cause alignment issues for the user.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>This defines an API with different behavior based on the
underlying transport in ways that are visible to the application. Add a
flag that specifies if immediate data is supported. Define one way of
doing that, and move on. I fail to see any benefit complicating the API
for a transport that has to emulate transferring immediate data in an application
visible way.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>- Sean</span></font><o:p></o:p></p>
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