Supercomputer on a Chip

Computerworld - Computer scientists at the University of Texas at Austin are inventing a radical microprocessor architecture, one that aims to solve some of the most vexing problems facing chip designers today. If successful, the Defense Department-funded effort could lead to processors of unprecedented performance and flexibility.
The density of transistors on a chip has doubled at least every two years for decades, and microprocessor designers have put those transistors to good use. Advanced circuits use techniques such as program branch prediction and speculative execution in order to build deep instruction "pipelines" that increase the throughput of the processor by allowing it to execute multiple instructions simultaneously. But the growing complexity of such circuits, and the heat they produce, signal an end to that approach. Rather than trying to build faster processor cores, chip builders are beginning to put more of them on a chip.
The problem with that, says Doug Burger, a computer science professor at the University of Texas, is that for application software to take advantage of those multiple cores, programmers must structure their code for parallel processing, and that's difficult or impossible for some applications. "The industry is running into a programmability wall, passing the buck to software and hoping the programmer will be able to write codes for their systems," he says.
Burger and his colleagues hope to solve these problems with a new microprocessor and instruction set architecture called Trips, or the Tera-op Reliable Intelligently Adaptive Processing System. "Our goal is to exploit concurrency, whether it's given to you by the programmer or not," he says.
Trips uses several techniques to do just that. First, the Trips compiler sends executable code to the hardware in blocks of up to 128 instructions. The processor "sees" and executes a block all at once, as if it were a single instruction, greatly decreasing the overhead associated with instruction handling and scheduling.
Second, instructions inside a block execute in a "data flow" fashion, meaning that each instruction executes as soon as its inputs arrive, rather than in some sequence imposed by the compiler or the programmer. "As such, the data is flowing through the instructions," explains Steve Keckler, a computer science professor and a Trips project co-leader with Burger.
Increasing Efficiency
Another trick: Within a block, the Trips compiler can merge two instructions that are on different paths into a single instruction if they have the same target and operation. Compared with earlier designs based on data flow concepts, "our aggressive data-flow model gives the compiler the opportunity to produce much tighter and more efficient code," says