[Beowulf] Clusters just got more important - AMD's roadmap

Eugen Leitl eugen at leitl.org
Wed Feb 8 08:39:24 PST 2012


On Wed, Feb 08, 2012 at 06:18:50AM -0800, Lux, Jim (337C) wrote:

> It can be done (and probably has), but it's going to be "exotic" and
> expensive.

There are some liquid metal (gallium alloy, strangely enough
not sodium/potassium eutectic which would be plenty cheaper
albeit a fire hazard if exposed to air) cooled GPUs for the 
gamer market. I might have also read about one which uses
a metal pump with no movable parts which utilizes MHD, though
I don't remember where I've read that.

There are also plenty of watercooled systems among enthusiasts,
including some that include CPU and GPU coolers in the same circuit.

I could see how gamers could push watercooled systems into
COTS mainstream, it wouldn't be the first time. Multi-GPU
settings are reasonably common there, so the PCIe would seem
like a good initial fabric candidate.
 
> >I don't see how x86 should make it to exascale. It's too
> >bad MRAM/FeRAM/whatever isn't ready for SoC yet.
> 
> 
> Even if you put the memory on the chip, you still have the interconnect
> scaling problem.  Light speed and distance, if nothing else.  Putting

You can eventually put that on WSI (in fact, somebody wanted to do
that with ARM-based nodes and DRAM wafers bonded on top, with
redundant routing around dead dies -- I presume this would also
take care of graceful degradation if you can do it at runtime,
or at least reconfigure after failure, and go back to last
snapshot). Worst-case distances would be then ~400 mm within
the wafer, and possibly shorter if you interconnect these with
fiber.

The only other way to reduce average signalling distance is real
3D integration.

> everything on a chip just shrinks the problem, but it's just like 15 years
> ago with PC tower cases on shelving and Ethernet interconnects.

Sooner or later you run into questions like "what's within the lightcone of a
1 nm device", at which point you've reached the limits of classical
computation, nevermind that I don't see how you can cool anything
with effective >THz refresh rate. I'm extremely sceptical about QC 
feasibility, though there's some work with nitrogen vacancies in 
diamond which could produce qubit entanglement in solid state, 
perhaps even at room temperature. I just don't think it would
scale well enough, and since Scott Aaronson also appears dubious 
I'm in good company.


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