<html><head><style type='text/css'>p { margin: 0; }</style></head><body><div style='font-family: Arial; font-size: 12pt; color: #000000'><BR><BR><FONT face="times new roman, new york, times, serif">>----- Original Message -----<BR>>From: "Jan Heichler" <jan.heichler@gmx.net><BR>>To: "richard walsh" <richard.walsh@comcast.net><BR>>Cc: beowulf@beowulf.org<BR>>Sent: Saturday, April 11, 2009 3:56:10 AM GMT -05:00 US/Canada Eastern<BR>>Subject: Re[2]: [Beowulf] Nehalem memory configs<BR>><BR>
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<P><FONT face="times new roman, new york, times, serif">>Hallo richard,</FONT></P>
<P><FONT face="times new roman, new york, times, serif">><BR></FONT></P>
<P><FONT face="times new roman, new york, times, serif">>Freitag, 10. April 2009, meintest Du:</FONT></P>
<P><FONT face="times new roman, new york, times, serif">><BR></FONT></P>
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<P><FONT face="times new roman, new york, times, serif"><BR></FONT></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">> Kilian CAVALOTTI wrote:</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>> On Wednesday 08 April 2009 19:48:30 Joe Landman wrote:</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> As an FYI, Beowulf veteran Jeff Layton wrote up a nice article on</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> memory</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> configuration issues for Nehalem (I had seen some discussion on this</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> previously).</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>></FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> Link is here:</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> http://www.delltechcenter.com/page/04-08-2009+-+Nehalem+and+Memory+Configur</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>>> ations</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>></FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>> That's a great write-up, gathering all the useful information in one</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">>> place. A must read. Thanks Jeff!</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">It is a good write up, very good ... but there looks to be an error under "Memory Bandwidth</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">Performance" ... first, for socket-local-memory, I am not sure of the relevance of</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">the QPI GT rate. I would calculate the maximum rate to socket-local-memory</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">with 1 DIMM per channel at:</FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif"></FONT></SPAN> </P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">1.333 GHz x 3 Channels x 8 bytes = 31.992 GBytes/sec </FONT></SPAN></P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif"></FONT></SPAN> </P>
<P><SPAN class=rvts6><FONT face="times new roman, new york, times, serif">not 35 GByters/sec. Maybe I am doing something wrong. ยด</FONT></SPAN></P></TD></TR></TBODY></TABLE></DIV>
<P><FONT face="times new roman, new york, times, serif">><BR></FONT></P>
<P><FONT face="times new roman, new york, times, serif">><BR></FONT></P>
<P><FONT face="times new roman, new york, times, serif">>I understood the 35 GB/s to be the transfer rate that you reach when</FONT></P>
<P><FONT face="times new roman, new york, times, serif">>accessing Memory with 8 Cores. So it involves 6 Channels (2 CPUs,</FONT></P>
<P><FONT face="times new roman, new york, times, serif">>3 channels each). ~64 GB/s (theory) - 35 GB/s (real life). Makes sense</FONT></P>
<P><FONT face="times new roman, new york, times, serif">>to me. </FONT></P>
<P><FONT face="times new roman, new york, times, serif"></FONT> </P>
<P><FONT face="times new roman, new york, times, serif">64 GB/sec is the right dual-socket theoretical number for this situation, and Intel</FONT></P>
<P><FONT face="Times New Roman">presents the value of 33 GB/sec for the stream triad for the dual socket boards,</FONT></P>
<P><FONT face="Times New Roman">so 35 GB/sec could be a copy perhaps, but nothing was mentioned about any</FONT></P>
<P><FONT face="Times New Roman">benchmark in the memory piece. In any case, I think we have the right theoretical</FONT></P>
<P><FONT face="Times New Roman">and probable real-world numbers expressed here, if people were wondering.</FONT></P>
<P><FONT face="Times New Roman"></FONT> </P>
<P><FONT face="Times New Roman">rbw </FONT></P><BR><FONT face="times new roman, new york, times, serif">_______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf </FONT></div></body></html>