Flynn s Taxonomy of Parallel Architectures

Transcription

1 Flynn s Taxonomy of Parallel Architectures Stefano Markidis, Erwin Laure, Niclas Jansson, Sergio Rivas-Gomez and Steven Wei Der Chien 1 Sequential Architecture The von Neumann architecture was conceived in the mid-1940s Arithmetic logic unit (ALU) is the heart of the computer, performing the actual computation. Registers can be read and written to at the speed of the surrounding logic. A bank of several registers allow for simultaneous reads and writes The processor accesses the main memory of the computer system to store and use the values of the program variables making up the state of the calculation. The operation of the processor is managed by the controller, which creates a sequence of signals to the hardware. Originally this was done as a series of phases: fetch instructions, execute operation, and write back to register (or memory). This would be repeated for each succeeding operation of the instruction stream. 2

2 Flynn's Taxonomy In the 1966, Michael Flynn proposed a taxonomy that simplified categorization of distinct classes of parallel architecture and control methods based on the relationships of data and instruction (control) Comprising four characters, it divides the world of computing structures into four classes in a 2D space. One dimension concerns the, D, whether there is one such stream, S, or multiple s, M. The other dimension relates to the control or instruction stream, I whether there is one instruction stream, S, or multiple instructions streams, M. SISD Single Instruction, Single Data MISD Multiple Instruction, Single Data SIMD Single Instruction, Multiple Data MIMD Multiple Instruction, Multiple Data 3 SISD single instruction stream, single data stream This represents the conventional sequential (serial) processor structure where a single thread of control, the instruction stream, guides the sequence of operations performed on a single set of data, one operand at a time 4

3 SIMD single instruction stream, multiple The first form of parallelism conveyed within Flynn s taxonomy is simultaneous operation on multiple datasets, controlled by the same set of instructions. Thus each operation at any one time is the same performed on different data arguments. Example of SIMD? 5 MIMD multiple instruction stream, multiple Like SIMD, there are many sets of data but in this case each dataset has its own instruction stream associated with it. At any one time there are many operations being performed, but they need not be the same and in fact are almost always different. As will be seen, this is the most widely used form of parallel architecture, but the category has many different subclasses. Example? 6

4 MISD multiple instruction stream, single Fourth of Flynn's categories is debated: One possible interpretation is a coarsegrained pipeline where each pipe stage accepts data from the previous stage, performs a set of operations on these data stream elements, and then passes on the results to the next stage. Another interpretation is a shared-memory multiprocessor where, as the name suggests, multiple processors each with its own instruction stream work on the same (therefore shared) data on which all the other processors operate. 7 SPMD Not strictly part of Flynn's taxonomy but related to and inspired by it. We will use it later SPMD stands for single program, multiple and reflects a practical variation of the SIMD model. Instead of issuing and broadcasting one instruction at a time to all the simple processing units of a SIMD-like machine, SPMD sends a function call of a coarse-grained procedure that is to be performed by all the processing units of the parallel machine. The invocation of heavyweight tasks rather than lightweight instructions: amortizes the overheads and latency times involved in system control 8

5 Conclusions Flynn s taxonomy categorizes different parallel architectures in terms of instruction and s that can be single or multiple Still in use today to categorize parallel architectures. Next week lectures you will use them 9