SiCortex Introduces “Green Computing Index” to Rank Big Computers on Energy Efficiency
There’s no such thing as a free flop.
A “flop,” or floating-point operation, is a calculation involving a decimal number; engineers often measure the performance of computers in terms of the number of “gigaflop/s” (billions of floating-point operations per second) they can sustain. In the supercomputing community, it’s a longstanding ritual to compare various machines’ maximum gigaflop/s as they tackle standardized math problems called benchmarks. The world’s fastest computer—a 122,400-processor IBM machine at the Los Alamos National Laboratory called Roadrunner—can run at just over a million gigaflop/s, or 1.026 petaflop/s, according to Top500, the most prominent list of top supercomputing sites.
But as a general rule, the faster a computer runs, the more power it consumes—and the more waste heat it generates, and the more additional power is needed to run cooling systems. If current trends continue, according to McKinsey & Company, then by 2020 the electric plants needed to power the world’s data centers will be churning out more greenhouse gases than the entire airline industry. The problem is getting so serious that some organizations are having to scale back plans to upgrade their data centers with faster machines—not because they can’t afford them, but because local utilities can’t supply any more electricity.
Maynard, MA-based SiCortex serves the high-performance computing market, so it’s naturally obsessed with the gigaflops game—but with a twist. The six-year-old startup builds massively parallel computers with thousands of processors. The processors themselves aren’t very fast. They run at around 700 Megahertz, slower than the chips inside most desktop and laptop PCs, which saves a lot of electricity. But they’re wired together in a way that makes SiCortex’s computers extremely zippy nonetheless. And today SiCortex is proposing an overhaul in the way the performance of high-end computers is measured and ranked, one that would take a machine’s power consumption into account and reward machines that use it sparingly.
The company calls its new measuring system the Green Computing Performance Index, and it’s urging managers of government and academic supercomputing centers and corporate data centers to use it to evaluate the full benefits and costs of owning high-performance computing systems from companies like Cray, SGI, Hewlett-Packard, IBM, and of course, SiCortex itself.
When evaluating the full cost of owning a high-performance computer, SiCortex argues, organizations should divide its performance in gigaflop/s by its power consumption in kilowatts. When you do that, a number of machines that are nominally faster than SiCortex’s machines—such Cray Inc.’s XT3 and XT4, IBM’s Blue Gene, and SGI’s Altix 8200EX—come out looking like power hogs. When running the standard Linpack benchmark, for example, an 1,100-processr Cray XT3 machine at the Swiss National Supercomputing Centre gets just 17 gigaflop/s to the kilowatt, while a 1,458-processor SiCortex machine gets a comparatively huge 253 gigaflop/s to the kilowatt.
“If you look at the high-performance computing benchmarks that Top500 produces, it’s great stuff, but it doesn’t give you a measure of the actual energy efficiency of the computers themselves,” says Christopher Stone, SiCortex’s CEO. “Everyone in the high-performance computing business is running around talking about being green or wanting to be green, so we thought why not create an index that actually gives you some measurement?” Just as you’d measure an automobile’s fuel efficiency by looking at its miles-per-gallon rating rather than its top speed, Stone argues, computer buyers should consider how much bang they’re getting for each buck they spend on electricity.
SiCortex’s index isn’t the first to rate computers on their green credentials. Wu-chun Feng, a computer scientist at Virginia Tech, introduced the Green500 list last November; it essentially re-orders the computers on the Top500 list according to their energy efficiency in megaflop/s per watt. But SiCortex argues that the Green500 list is inadequate, since the Top500 performance statistics are based solely from the Linpack benchmark, which tends to reward CPU speed over other factors such as the speed of memory subsystems and of the communications network connecting processors. As I explained in a September profile, SiCortex’s machines get most of their speed boost from their backplanes, the communications meshes linking all their processors—explaining why the company is basing its proposed index on the HPC Challenge, a broad collection of seven benchmarks devised by the Defense Advanced Research Projects to measure computers’ performance in real-world situations.
You probably won’t be surprised to learn that SiCortex computers compare very well to competitors’ machines in statistics distributed by the company today. In one chart, SiCortex’s 1,458-processor machine bested not only the Swiss Cray XT3 on the Linpack component of the Green Computing Performance Index, but also beat an IBM Blue Gene computer at the San Diego Supercomputer Center (136 gigaflop/s per kilowatt), an SGI Altix ICE 8200EX system a the Dresden University of Technology (232 gigaflop/s per kilowatt) and a Cray XT4 system at the U.S. Army Corp of Engineers’ Major Shared Resource Center (130 gigaflop/s per kilowatt).
“We obviously come out pretty well, because of the way we designed our machines,” says Stone. “But there are cases where we don’t come out on top. And maybe somebody will produce data that make us look terrible. That’s fine—we’re providing everybody with the data we used and where we got, so that they can go off and find what’s wrong.”
And as it turns out, SiCortex’s machines are not the greenest around. When IBM’s Roadrunner is running at 1.026 petaflop/s, for example, it consumes 2,346 kilowatts of power, which comes to an extremely efficient 437 gigaflop/s per kilowatt, earning it the #3 spot in the Green500 list. That’s almost twice as efficient as a 1,458-processor SiCortex machine. Of course, 2,346 kilowatts is an immense amount of power—equal to the output of two or three nuclear power plants—and not too many organizations can afford Roadrunner’s $100 million price tag.
Stone says SiCortex hopes to find an neutral, outside organization to take over administration of the Green Computing Performance Index—and mentions Jack Dongarra, the creator of the Top500 list, as a candidate. “We’d be happy to work with him,” says Stone. “Or if a new body of people wanted to get together and formulate a new index around this data, but maybe call it something different or measure in a different way, we’d be happy to go along with that. Debate is healthy, and we need a good debate about how to measure the computing industry’s carbon footprint.”
Addendum 11/7/08: HPCwire’s John West published a nice feature yesterday on SiCortex and the Green Computing Performance Index.