Unit17-PerformanceModeling-EE357-Nazarian-Fall09

Unit17-PerformanceModeling-EE357-Nazarian-Fall09 -...

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University of Southern California Viterbi School of Engineering EE357 asic Organization of Computer Systems Basic Organization of Computer Systems erformance Modelin Performance Modeling References: 1) Textbook Shahin Nazarian Fall 2009 2) Mark Redekopp’s slide series
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An Opening Question An Intel and a Sun/SPARC computer measure eir respective rates of instruction execution on their respective rates of instruction execution on the same application written in C Computer A achieves 160 MIPS (Millions of Instructions Per Second) Computer B achieves 200 MIPS hich computer executes the program faster? Which computer executes the program faster? It depends on the instruction set and compiler (ultimately, the instruction count). Computer B and its compiler may use many more simpler (faster) instructions to implement the program thereby increasing its instruction execution rate but saying othing of overall execution time Shahin Nazarian/EE357/Fall 2009 2 nothing of overall execution time
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Another Question A Pentium 3 has a clock rate of 1 GHz while a Pentium 4 has a clock rate of 2 GHz They implement the same instruction set hey are tested on the same executable program They are tested on the same executable program Is the Pentium 4 twice as fast as the Pentium 3? Since they both use the same instructions and the same instruction count (same executable), we may think that the Pentium 4 would be twice as fast However, the microarchitectural implementation of the processor may mean that the Pentium 3 executes instructions in 2 clocks on average while the Pentium 4 executes instruction in 4 clocks on average thus making Shahin Nazarian/EE357/Fall 2009 3 the execution time exactly the same
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Execution Time Execution time Execution time (and not the clock rate and # of instructions per sec by themselves) is the valid metric for comparing performance Two possible performance goals Execution time : Measured for a single program’s execution Throughput : Total jobs jobs performed per unit time Shahin Nazarian/EE357/Fall 2009 4
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Wall Clock Time vs. CPU Time Even execution time can be hard to measure accurately because the OS may allocate a percentage of compute cycles to other programs (also, part of a program’s execution time is spent in OS calls for I/O, etc.) ll Cl ck Time Re l time it t k fr m Wall Clock Time : Real time it took from when the user submitted the job until it was completed CPU Time : Actual time the program took to execute when it was running Shahin Nazarian/EE357/Fall 2009 5
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Performance Performance is defined as the inverse of execution time Time Execution 1 e Performanc = Often want to compare relative erformance or speedup (how many times performance or speedup (how many times faster is a new system than an old one) New Old Old New Execution Execution e Performanc e Performanc Speedup = = Shahin Nazarian/EE357/Fall 2009 6
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Performance Equation Execution time can be modeled using three components Instruction Count
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Unit17-PerformanceModeling-EE357-Nazarian-Fall09 -...

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