Brice,
You're talking only about latency, right? From the graphs FDR/Gen3 and
QDR/Gen3 are almost identical.
For bandwidth, QDR/Gen3 provided only a 16 - 20% improvement over
QDR/Gen2., depending on whether they were measuring one-way or
bidirectional bandwidth, whereas FDR seemed to provide about 40-50 % of
the bandwidth performance difference between FDR/Gen3 and QDR/Gen2.
Interestingly, the text of the article didn't compare FDR/Gen3 to
QDR/Gen3, but it's clear from the graphs that FDR/Gen 3 is still way
above QDR/Gen3 despite the 16-20% improvement Gen3 provides.
Prentice
On 10/30/2014 11:08 AM, Brice Goglin wrote:
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
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