On Fri, 31 Oct 2014 01:17:49 -0400 (EDT) Mark Hahn <h...@mcmaster.ca> wrote:
> > If you compare QDR devices to FDR devices, than FDR is showing lower > >latency. > > in the paper referenced, that is not the case. the numbers provided > are QDR 1.27 us, versus FDR 1.67 us. although it's only 400ns, > it's still >30% slower, when one might expect a speed improvement. These numbers match almost perfectly with the numbers in my other e-mail. That is, 1.27 is QDR on pre-sandy bridge systems and 1.67 is the far socket on a sandy bridge. If that's the case then the "slow FDR" observation is really the pci-e suckiness over QPI on sandy bridge. ... > that's interesting - do you mean that in order to achieve higher > bandwidth, the error rate becomes a problem, necessitating RT/FEC? I > guess it's obvious from the shrinkage of allowed passive/copper cable > lengths that SNR/BER is a big issue, but does this imply that going > optical will reduce the latency cost for FDR? Optical cables are not a magic fix-all. We have much better reliability and lower BER on our FDR cupper vs our EoE. /Peter _______________________________________________ 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
