[Beowulf] ARM cpu's and development boards and research

Eugen Leitl eugen at leitl.org
Tue Nov 27 23:40:47 PST 2012

On Tue, Nov 27, 2012 at 06:17:55PM -0500, Prentice Bisbal wrote:
> On 11/27/2012 03:37 PM, Douglas Eadline wrote:
> >
> >> My interest in Arm has been the flip side of balancing flops to network
> >> bandwidth.  A standard dual socket (AMD or Intel) can trivially saturate
> >> GigE.  One option for improving the flops/network balance is to add
> >> network bandwidth with Infiniband.  Another is a slower, cheaper, cooler
> >> CPU and GigE.
> >>
> > applause.
> I applaud that applause.
> What Bill has just described is known as an "Amdahl-balanced system", 
> and is the design philosophy between the IBM Blue Genes and also 
> SiCortex. In my opinion, this is the future of HPC. Use lower power, 

The laws of the universe agree with your opinion. A provably optimal
classical computing configuration requires a close packing of the nodes
so that they're within each other light cones to minimize communication
latency. A sea of nodes on a mesh is will approach that asymptotically,
by shrinking the grain size until the units of memory and computation
is identical. Notice that you don't need a global clock, as local
communication can be asynchronous, and in general a locally weakly
coupled system of oscillators will synchronize soon after bootup, until
they beat in unison. 

Your problem is mapped to a virtual circuit trace, laid out in
a 3d volume, with a volume refresh rate commensurable with
geometry of the light cone, which has a physical limit of about ~nm.

I also hope that spintronics, both for storage (MRAM) and computation
will reduce the power envelope, and also increase reliability (e.g.
spintronics is effectively immune to radiation).

> slower processors, and then try to improve network performance to reduce 
> the cost of scaling out. Essentially, you want the processors to be 
> *just* fast enough to keep ahead of the networking and memory, but no 
> faster to optimize energy savings.
> The Blue Genes do this incredibly well, so did SiCortex, and Seamicro 
> appears to be doing this really well, too, based on all the press 
> they've been getting. With the DARPA Exascale report saying we can't get 
> to Exascale with current power consumption profiles, you can bet this 
> will be a hot area of research over the next few years.
> Okay. I'm done listening to myself type.

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