Re: Roadrunner Supercomputer using 12,960 CELL Processors Hits 1

On Jun 11, 5:22 am, already5cho...@[EMAIL PROTECTED]
 wrote:

>
> I'd agree with mr deo.
> Roadrunner interconnects look like a big step backward from other PR-
> heavy American supercomputers.

http://www.lanl.gov/orgs/hpc/roadrunner/pdfs/Kerbyson%20-%20RR%20Modeling,%20Performance%20&%20Results/031908_RR_model.pdf

The predicted worst-case latency is about the same as Blue-Gene.  Red
Storm routing/switching looks like Blue Gene.  Columbia uses both
Infiniband and Numalink in a fat tree like Roadrunner.

> Hopefully, they are not as boring as in
> Virginia Tech cluster that you mentioned, but not in the same class as
> Cray/Sandia Red Storm, SGI/NASA Columbia or IBM/LLNL BlueGene/L.
>
Could you be more specific than, "Hopefully they are not as boring?"
Blue Gene and Red Storm have an interconnect topology that's fine for
problems with good locality.  Not so good for problems requiring
global communication.  Columbia and Roadrunner use fat trees, much
better for the problems that interest me the most.

> Also it looks like programming model for Roadrunner (3 separate
> architecture and many programmer-visible levels of memory hierarchy)
> is much harder to use effectively than just about any big
> supercomputer built up to date.
>
Coprocessors are here to stay.  At the moment, they will be painfully
visible to the programmer.

> Last, but not least, performance per watt and per cubic meter seem
> seriously worse than BlueGene.

Not im****tant for the time being.  FP-intensive coprocessors can be
very effective in flops/watt.  Neither the OOO-processor nor the FP
coprocessor was optimized for power performance.  The more im****tant
point, for the moment, is to show that all those flops can actually be
put to use.

To get back to the previous poster's point, building a machine with
lots of flops requires only money.  Actually using those flops for
something other than linpack  is another matter.

Robert.