Vector Computers - 大连理工大学精品课程建设工程.ppt

Computer ArchitectureVector Computers contents 1. Why Vector Processors? 2. Basic Vector Architecture 3. How Vector Processors Work 4. Vector Length and Stride 5. Effectiveness of Compiler Vectorization 6. Enhancing Vector Performance 7. Performance of Vector Processors Vector Processors I’m certainly not inventing vector processors. There are three kinds that I know of existing today. They are represented by the Illiac-IV, the (CDC) Star processor, and the TI (ASC) processor. Those three were all pioneering processors. . . . One of the problems of being a pioneer is you always make mistakes and I never, never want to be a pioneer. It’s always best to come second when you can look at the mistakes the pioneers made. Seymour Cray Public lecture at Lawrence Livermore Laboratories on the introduction of the Cray-1 (1976) Supercomputers Definition of a supercomputer: Fastest machine in world at given task A device to turn a compute-bound problem into an I/O bound problem Any machine costing $30M+ Any machine designed by Seymour Cray CDC6600 (Cray, 1964) regarded as first supercomputer Supercomputer Applications 1. Why Vector Processors? A single vector instruction specifies a great deal of work—it is equivalent to executing an entire loop. The computation of each result in the vector is independent of the computation of other results in the same vector and so hardware does not have to check for data hazards within a vector instruction. Hardware need only check for data hazards between two vector instructions once per vector operand, not once for every element within the vectors. Vector instructions that access memory have a known access pattern. Because an entire loop is replaced by a vector instruction whose behavior is predetermined, control hazards that would normally arise from the loop branch are nonexistent. 2. Basic Vector Architecture There are two primary types of architectures for vector processors: vector-register processors and memory-memory vector