1 Why parallelism CMU 15-418/618 23sp https://www.bilibili.com/video/BV1SM4y1j7XL/ 1 Why parallelism A Brief History of Process Performance initial focus: 1.supercomputer for scientific computing(1970s) 2.database(1990s) Wider data paths: 4 bit to 64 bit More efficient pipelining: increasing CPI Exploiting ILP: superscalar processing example of ILP : pipelining, superscalar execution, VLIW(Very Long Instruction Word), vector processing, Out of order execution Faster clock rates: 3GHz Obstacles: Power Density Wall, No further benifit from ILP, Processor clock rate stops increasing What is a parallel computer definition: a collection processing elements that cooperate to solve problems quickly (efficiency & performance) Motivation: Speedup Speedup(P cores)=execution time(1 core)/execution time(P cores) influence factor : Communicati...