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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>PCIe Gen2 at 5GT, and 8/10 bit encoding and current chipsets efficiencies
gives you around 3.3GB/s per direction, so one IB QDR port can handle that. For
more BW out of the host, you can use more adapters (single port ones are the
cost effective solution for that). <o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Gilad<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p> </o:p></span></p>
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<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span></b><span
style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'>
beowulf-bounces@beowulf.org [mailto:beowulf-bounces@beowulf.org] <b>On Behalf
Of </b>Brian Dobbins<br>
<b>Sent:</b> Tuesday, February 23, 2010 2:42 PM<br>
<b>To:</b> Patrick Geoffray<br>
<b>Cc:</b> beowulf@beowulf.org<br>
<b>Subject:</b> Re: [Beowulf] Q: IB message rate & large core counts (per
node)?<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> I thought PCIe Gen2 x 8 @ 500 Mhz gives 8GB/s?
I know there are 250 and 500 Mhz variants in addition to the lane sizes, so
while a 250 Mhz x8 link wouldn't provide enough bandwidth to a dual-port card,
the 500 Mhz one should. But I'm woefully out of date on my hardware
knowledge, it seems. Of course, EDR (eight data-rate) IB is on the
roadmap for 2011, so if we're in no rush that could help, too.<o:p></o:p></p>
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<p class=MsoNormal style='margin-bottom:12.0pt'><br>
Er,.. I thought about this a half-second after I sent it. First, that's
5.0 Ghz, not 500 Mhz, and second, that's probably aggregate bi-directional
throughout at 8 GB/s, isn't it? So, I got it, 4 GB/s per direction, which
means dual-port won't get us much in terms of unidirectional throughput.<br>
<br>
- Brian<o:p></o:p></p>
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