[Beowulf] InfiniBand channel bundling?

[Gilad Shainer]

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-bounces at 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.sassmannshausen at 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