[Beowulf] InfiniBand channel bundling?

Jörg Saßmannshausen j.sassmannshausen at ucl.ac.uk
Wed Oct 29 15:43:54 PDT 2014

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


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

email: j.sassmannshausen at ucl.ac.uk
web: http://sassy.formativ.net

Please avoid sending me Word or PowerPoint attachments.
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