Slashdot Mirror
The Supercomputer Race
CWmike writes "Every June and November a new list of the world's fastest supercomputers is revealed. The latest Top 500 list marked the scaling of computing's Mount Everest — the petaflops barrier. IBM's 'Roadrunner' topped the list, burning up the bytes at 1.026 petaflops. A computer to die for if you are a supercomputer user for whom no machine ever seems fast enough? Maybe not, says Richard Loft, director of supercomputing research at the National Center for Atmospheric Research in Boulder, Colo. The Top 500 list is only useful in telling you the absolute upper bound of the capabilities of the computers ... It's not useful in terms of telling you their utility in real scientific calculations. The problem with the rankings: a decades-old benchmark called Linpack, which is Fortran code that measures the speed of processors on floating-point math operations. One possible fix: Invoking specialization. Loft says of petaflops, peak performance, benchmark results, positions on a list — 'it's a little shell game that everybody plays. ... All we care about is the number of years of climate we can simulate in one day of wall-clock computer time. That tells you what kinds of experiments you can do.' State-of-the-art systems today can simulate about five years per day of computer time, he says, but some climatologists yearn to simulate 100 years in a day."
Is how many libraries of congress it can read in a fortnight.
Flops wouldn't test how well the interconnects work.
Since you say "increase the resolution of the model", you are expanding the size of the model, and how much data must be used by all of the nodes of the computer.
Since how important the interconnect properties are is dependent on the model, with almost no communication needed, like for F@H, to a problem that needs all of the nodes to have access to a single shared set of data, it would be very hard to quantify performance in one number.
Unfortunately, there are more than a few fields where marketers want a single number to advertise in a "mine is bigger than yours" competition, and come up with a metric that is almost worthless.
If I have nothing to hide, don't search me
44 years ago 1-5 megaflops was hot! What excitement we felt when the CDC6600 was installed at my university!
Back in '85 I was part of a startup building a mini-Cray, reimplementing the Cray instruction set in a smaller, cheaper box. I remember we focused on the Whetstone benchmark a lot, and it turned out that the Whetstone code really was bound up by moving characters around while formatting output strings, etc. We paid very careful attention to efficiently coding the C library string handling routines, and that got us more performance payback than anything we could do to optimize the arithmetic. One needs to understand the benchmark being used.
It's about a half a petaflop... but guess what? It runs Linux!
This sounds kind of nice but why should this make it any easier to write parallel programs for it? You still have to manage hundreds if not thousands of threads, right? This will not magically turn it into a computer for the masses, I guarantee you that. I have said it elswhere but parallel computing will not come of age until they do away with multithreading and the traditional CPU core. There is a way to build and program parallel computers that does not involve the use of threads or CPUs. This is the only way to solve the parallel programming crisis. Until then, supercomputing will continue to be a curiosity that us mainstream programmers and users can only dream about.