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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Prentice Bisbal
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Rutgers Discovery Informatics Institute (RDI2)
Rutgers University
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