[Beowulf] Broadcast - not for HPC - or is it?

[Daniel Kidger]

  Matt,

Are you really claiming <9ns port to port ?
(Quadrics used to think they were leading edge with 40ns latency port to 
port latency on their switches)

At <9ns for the 'switch' then surely the speed of light in copper (a 
massive 1ns per foot) will dominate over the switch itself?


Plus as others say it is not the broadcast that is the hard bit - it is 
getting the consolidated acks back.

Daniel


> I'm associated with a somewhat stealthy start-up.  Only teaser product
> with some details out so far is a type of packet replicator.
>
> Designed 24 port ones, but settled on 16 and 48 port 1RU designs as
> this seemed to reflect the users needs better.
>
> This was not designed for HPC but for low-latency trading as it beats
> a switch in terms of speed.  Primarily focused on low-latency
> distribution of market data to multiple users as the port to port
> latency is in the range of 5-7 nanoseconds as it is pretty passive
> device with optical foo at the core.  No rocket science here, just
> convenient opto-electrical foo.
>
> One user has suggested using them for their cluster but, as they are
> secretive about what they do, I don't understand their use case.  They
> suggested interest in bigger port counts and mentioned>1000 ports.
>
> Hmmm, we could build such a thing at about 8-9 ns latency but I don't
> quite get the point just being used to embarrassingly parallel stuff
> myself.  Would have thought this opticast thing doesn't replace an
> existing switch framework and would just be an additional cost rather
> than helping too much.  If it has a use, may we should build one with
> a lot of ports though 1024 ports seems a bit too big.
>
> Any ideas on the list about use of low latency broadcast for specific
> applications in HPC?  Are there codes that would benefit?
>
> Regards,
>
> Matt.
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-- 
Bull, Architect of an Open World TM

Dr. Daniel Kidger, HPC Technical Consultant
daniel.kidger at bull.co.uk
+44 (0) 7966822177