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Has Supercomputing Hit a Brick Wall?
anzha writes "Horst Simon, Deputy Director of Lawrence Berkeley National Laboratory, has stood up at conferences of late and said the unthinkable: supercomputing is hitting a wall and will not build an exaFLOPS HPC system by 2020. This is defined as one that passes linpack with a performance of one exaFLOPS sustained or better. He's even placed money on it. You can read the original presentation here."
moore's law only talks about transistor counts. building a supercomputer means getting thousands of CPUs to cooperate which is a much harder challenge.
Anyone (with a large wallet) can stick an exoflop worth of CPUs in a large room. by 2020 you'll be able to do that with a not so large wallet. but that does not result in a useful exoflop computer
It's a particular nuisance because the speed of light is pretty strictly enforced...
Even if you went full-on-nuts and replaced fiber interconnects with little tubes full of hard vacuum, to squeak out that slight improvement over the speed of light in glass or air, you'll still see latency that meaningfully hinders the cooperation of multi-GHz CPUs and RAM across systems of any nontrivial size.
For loosely coupled problems, that barely matters; but not all problems are loosely coupled.
I'm no expert on the refined world of supercomputers; but my money would be on latency. If you are made of money, bandwidth is a problem that you can substantially brute force. Not 100% efficiently; and layout gets to be a real headache; but if the state of the art in serial interconnects isn't good enough, you can bolt a bunch of them together and have a parallel interconnect(it'll be harder to do board layout for, the wiring will suck more, and it'll cost more; but the major sticking point is money).
If you want to cut latency, even the most exotic photonics-on-die-with-hollow-fiber arrangement imaginable still gives you surprisingly short distances before you start losing CPU cycles to waiting for the return photon.
I'm an HPC professional, and do not see much value in these "hero" machines. Yes, you can go on all you want about the march of progress and tier-1 and grand challenges, but you're just reiterating an unquestioned manifest destiny-based view of history. Why do we need an Exaflop machine? is it because some particular set of applications need it? where is the threshold for those applications where the compute facility will be fast enough to achieve some breakthrough?
it's hard to find areas that are primarily limited by compute facilities. for instance, genetics/proteomics/metabilomics/whatever are *not* compute-limited, especially at the high end. they're laboratory-limited, the same way weather simulations are good and getting better, but not past the quality of their input data.
we need more compute in general, but not necessarily in one machine. a single exaflop machine will cost much more than a thousand petaflop machines. letting a thousand flowers bloom is much prettier than one excruciatingly beautiful flower...
and no, hero machines do not provide an efficient way to improve the tech of lesser or later machines. they have to be justified by their own need.