Do you want to compare FDR vs QDR when used in the exact same PCIe slots? FDR often goes in Gen3 while QDR has been in Gen2 for a while.
According to the link below, Gen3 is responsible for pretty much all the improvement between QDR/Gen2 and FDR/Gen3. http://en.community.dell.com/techcenter/high-performance-computing/b/general_hpc/archive/2012/03/06/hpc-i-o-performance-using-pci-e-gen3-slots-on-the-12th-generation-12g-poweredge-servers Brice Le 30/10/2014 15:41, Prentice Bisbal a écrit : > Gilad, > > If end-to-end is lower for FDR, then what latency is being measured > for FDR that is higher than for QDR? According to Wikipedia, and the > Mellanox website, FDR does have a better latency than QDR (0.7 > microseconds vs. 1.3 microseconds), but I and others on this list have > heard that FDR has worse latency than QDR. Have we been misinformed, > or does it depend on how you measure or define latency? > > http://en.wikipedia.org/wiki/InfiniBand > http://www.mellanox.com/page/performance_infiniband > > Prentice > > > On 10/29/2014 06:46 PM, Gilad Shainer wrote: >> End-to-end FDR latency is lower than end-to-end QDR latency - per >> published measurments that can be found in multiple places. >> >> Gilad >> >> -----Original Message----- >> From: Beowulf [mailto:beowulf-boun...@beowulf.org] On Behalf Of Jörg >> Saßmannshausen >> Sent: Wednesday, October 29, 2014 3:45 PM >> To: Beowulf Mailinglist >> Subject: Re: [Beowulf] InfiniBand channel bundling? >> >> Hi all, >> >> thanks again for the wealth of information. >> >> Now, given that I am not interested in transporting files over the IB >> network but I am doing parallel calculations, I would have thought >> that the latency here is more important than the speed? >> Thus, if FDR has a higher latency than QDR, does that mean my >> performance is decreasing when I am running a calculation between nodes? >> >> For those of you who are into Chemistry code: I am using VASP, cp2k, >> quantum espresso and cpmd mainly. All of that is plain wave code. >> >> All the best from a wet London >> >> Jörg >> >> >> On Mittwoch 29 Oktober 2014 Prentice Bisbal wrote: >>> On 10/28/2014 04:43 PM, Mark Hahn wrote: >>>> On Tue, 28 Oct 2014, John Hearns wrote: >>>>> Here is a very good post from Glenn Lockwood regarding FDR versus >>>>> dual-rail QDR: >>>>> >>>>> http://glennklockwood.blogspot.co.uk/2013/05/fdr-infiniband-vs-dual >>>>> -rail >>>>> -qdr.html >>>> indeed, very nice. though also quite surprising - is it known that >>>> FDR is so terrible for latency? seems astonishing to me. >>> Yes, it was known to me. I had already known that FDR was worse than >>> QDR for latency, but I don't remember my source. I don't know if I'd >>> characterize it as "so terrible", though. >> >> -- >> ************************************************************* >> Dr. Jörg Saßmannshausen, MRSC >> University College London >> Department of Chemistry >> Gordon Street >> London >> WC1H 0AJ >> >> email: j.sassmannshau...@ucl.ac.uk >> web: http://sassy.formativ.net >> >> Please avoid sending me Word or PowerPoint attachments. >> See http://www.gnu.org/philosophy/no-word-attachments.html >> _______________________________________________ >> 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 > _______________________________________________ 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
