[Beowulf] Infiniband modular switches

Gilad Shainer Shainer at mellanox.com
Thu Jul 10 18:43:36 EDT 2008


Patrick Geoffray wrote: 

> > Not only that I was there, but also had conversations 
> afterwards. It 
> > is a really "fair" comparison when you have different injection 
> > rate/network capacity parameters. You can also take 10Mb 
> and inject it 
> > into 10Gb/s network to show the same, and you always can create the 
> > network pattern to show what you want to show, but you prove nothing
> 
> The injection rate is irrelevant 

The injection rate is super relevant. If your injection rate is 10% of
the fabric capability, or 100% of the fabric capability, the histogram
will be different. It was proven by the same person who did the slides
you referred to, when doing the same testing on IB DDR we got much
better results with IB versus Quadrics. your theory does not really meet
reality. Also, when you do look on adaptive routing, make sure it is
real time solution...  Not some synthetic testing .... 

<snip>


> 
> So far, IB only used static routing. If it still relies on 
> packet order on the wire for a given Queue Pair, then the 
> only way to do some sort of adaptive routing is to use a 
> different QP for each possible route (LID). 
> This is what Panda's group tried in a paper. However, the 
> number of QP explodes, each QP is still subject to HOL 
> blocking and the QP interleaving is static.
> 

What Panda did is using multiple static routs, which can be chosen
according to different algorithms. It is an interesting idea, and used
in several cases with nice results. This is not adaptive routing. 


Gilad.

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