Assessing and Understanding Performance B Ramamurthy Chapter 4 Defining Performance Airplane Passenger Capacity Cruising Range Cruising Speed mph Passenger throughput passengers X mph Boeing 777 375 4630 610 228 750 Boeing 747 470 4150 610 286 700 Concorde 132 4000 1350 178 200 DC 8 50 146 8720 544 79 424 Measuring Performance Time elapsed time response time Clock rate Clock cycles events in the system takes place precisely according to a clock that runs at constant time CPU execution time CPU clock cycle for a program X Clock cycle time Improving Performance A program runs in 10 seconds on computer A which has a 4 Ghz clock We want to build another computer B that will run program in 6 seconds We can increase the clock rate of but this affects the number of clock cycles of B and it is now 1 2 times that of B What is the clock rate of B CPU clock cycles instructions X average clock cycles per instructions Performance Equation CPU Time CPU Clock cycles X Clock cycle Time Inst Count X CPI X Clock cycle time Inst Count X CPI clock rate Algorithm affects instruction count Programming language affects instruction count and CPI Compiler instruction count and CPI Instruction set architecture Instruction count clock rate CPI Lets look at the examples in pages 252 253 SPEC Benchmarks System Performance Evaluation Corporation SPEC Latest release is a suite of programs 12 integer and 14 floating point programs CINT and CFP measure the geometric means of the performances of the CPU for the benchmarks See Figure 4 5 SPECweb99 a throughput benchmark for Web Servers