1. Vector/Array ProcessorsCSCI 4717 – Computer Architecture CSCI 4717/5717 Computer Architecture Topic: Vector/Array Processors Reading: Stallings, Section 18.7

2. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Computing Optimized for calculation rather than multitasking and I/O Design focus is to perform parallel mathematical operations on a vector or array of data elements Scalar processor would need to handle one element at a time. Limited market -- Research, government agencies, meteorology

3. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Computing (continued) Target applications: –data-intensive/scientific research such as: Aerodynamics, seismology, meteorology Continuous field simulation –specialized (high-performance) graphics applications Applicable because of ever-increasing need for improved resolution and model capabilities

4. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Array Processor Alternative to supercomputer Configured as a peripheral to mainframe or minicomputer Processor is only responsible for running vector portion of problem The Sony PlayStation 3 uses a processor consisting of one scalar processor and eight vector processors. Developed by IBM, Toshiba and Sony. (Source: http://en.wikipedia.org/wiki/Vector_computer)

5. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Operation Power of vector computing comes in the form of special processing instructions (Single Instruction, Multiple Data or SIMD) Lock-step execution of code issuing single instruction to a large number of identical processors (or ALUs) with a large register set working on different data elements Single master CPU keeps control of the entire process

6. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Speed-Up Not Linear As with any parallel processing architecture, the realized speed up of a vector processor is not linear because of: –Overhead for managing parallel computations –Bottlenecks for communication and storage –Load of application doesn't always match available processors These problems have an increasing effect with increases in the number of processors

7. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Data Pipelining The sequential nature of instructions allows for an instruction pipeline Vector computing tends to have data that is well organized too This allows for pipelining the data too Single decode for instruction Stages to fetch data, process data, store result in register

8. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Data Pipelining (continued) Example: To add an array of numbers, processor must have the following information: –a single "add" instruction –start address for the data –end address for the data

9. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Programming The programming goal is to divide a large dataset into independent sets that can be operated on in parallel Requires a deep understanding of the algorithm being applied to the data Distribute data to different processors Initiate parallel processing Bring everything back together when parallel processing is complete

10. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Programming (continued) Example: Count the number of times a specific value appears in a large array Begin by breaking up array into smaller arrays, one for each array processor Each array processor, in parallel, counts the number of occurrences of the value Final sum is then computed by adding the results from all of the processors

11. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Vector/Array Applications Which of the following applications would be better served by a vector or array computer than an SMP, cluster, or scalar processor? What component of the problem is parallel? –Web search indexing –Generating Fibonacci Sequence: f(i) = f(i-1) + f(i-2) –Weather prediction –Image processing for a game –Web site server –Photoshop-type image processing

12. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Scalar Programming The following two slides are based on the multiplication of two 100X100 matrices A and B DO 100 I = 1,N DO 100 J = 1,N C(I,J) = 0.0 DO 100 K = 1,N C(I,J) = C(I,J) + A(I,K)*B(K,J) (J = 1,N) 100CONTINUE

13. Vector/Array ProcessorsCSCI 4717 – Computer Architecture (J = 1,N) Vector Programming The notation (J = 1,N) indicates that operations on all indices J are to be carried out on N processors as a single operation DO 100 I=1,N C(I,J) = 0.0 (J = 1,N) DO 100 K = 1,N C(I,J) = C(I,J) + A(I,K)*B(K,J) (J = 1,N) 100 CONTINUE

14. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Fork/Join Parallel Programming One method of parallel programming is the fork-join. Programs start as a single process known as a master thread The operation "fork" is used to indicate the beginning of sections of the program that are to be executed in parallel The operation "join" is used to terminate the parallel threads created by "fork" to bring the program back to a single, master thread

15. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Fork/Join Method (continued) DO 50 J=1,N – 1 FORK 100 50CONTINUE J = N 100DO 200 I=1,N C(I,J) = 0.0 DO 200 K = 1,N C(I,J) = C(I,J) + A(I,K)*B(K,J) 200 CONTINUE

16. Vector/Array ProcessorsCSCI 4717 – Computer Architecture Neural Networks

17. Vector/Array ProcessorsCSCI 4717 – Computer Architecture What?! A Blank Slide?! It must be over!!!