PowerPoint PresentationReviewWhat is Time?How to Measure Time?Measuring Time using Clock Cycles (1/2)Measuring Time using Clock Cycles (2/2)Performance Calculation (1/2)Performance Calculation (2/2)How Calculate the 3 Components?Calculating CPI Another WayExample (RISC processor)What Programs Measure for Comparison?BenchmarksExample Standardized Benchmarks (1/2)Example Standardized Benchmarks (2/2)Example PC Workload BenchmarkPerformance EvaluationPerformance Evaluation: The DemoMegahertz Myth Marketing MoviePC / PC / Mac Showdown!!! (1/4)PC / Mac Showdown!!! (2/4)PC / Mac Showdown!!! (3/4)PC / Mac Showdown!!! (4/4)AdministriviaPeer InstructionPeer Instruction Answers“And in conclusion…”CS61C L41 Performance II (1)Garcia © UCBLecturer PSOE Dan Garciawww.cs.berkeley.edu/~ddgarciainst.eecs.berkeley.edu/~cs61c CS61C : Machine StructuresLecture 41 Performance IIUWB…Ultra Wide Band! www.nytimes.com/2005/05/04/technology/techspecial/04markoff.htmlThe FCC moved one step closer to approving a standard for this technology which uses spread spectrum pulses to send its information. Imagine no data wires to ANY of your devices!CS61C L41 Performance II (2)Garcia © UCBReview•RAID •Motivation: In the 1980s, there were 2 classes of drives: expensive, big for enterprises and small for PCs. They thought “make one big out of many small!”•Higher perf with more disk arms per $•Raid 0 through 5 are solutions with tradeoffs•32 B$ industry•Started @ Cal by CS Profs Katz & Patterson•Latency v. Throughput•Time for one job vs aggregate time for manyCS61C L41 Performance II (3)Garcia © UCBWhat is Time?•Straightforward definition of time: •Total time to complete a task, including disk accesses, memory accesses, I/O activities, operating system overhead, ...•“real time”, “response time” or “elapsed time” •Alternative: just time processor (CPU) is working only on your program (since multiple processes running at same time)•“CPU execution time” or “CPU time”•Often divided into system CPU time (in OS) and user CPU time (in user program)CS61C L41 Performance II (4)Garcia © UCBHow to Measure Time?•User Time seconds•CPU Time: Computers constructed using a clock that runs at a constant rate and determines when events take place in the hardware•These discrete time intervals called clock cycles (or informally clocks or cycles)•Length of clock period: clock cycle time (e.g., 2 nanoseconds or 2 ns) and clock rate (e.g., 500 megahertz, or 500 MHz), which is the inverse of the clock period; use these!CS61C L41 Performance II (5)Garcia © UCBMeasuring Time using Clock Cycles (1/2)•or= Clock Cycles for a program Clock Rate•CPU execution time for a program = Clock Cycles for a program x Clock Cycle TimeCS61C L41 Performance II (6)Garcia © UCBMeasuring Time using Clock Cycles (2/2)•One way to define clock cycles:Clock Cycles for program = Instructions for a program (called “Instruction Count”) x Average Clock cycles Per Instruction (abbreviated “CPI”)•CPI one way to compare two machines with same instruction set, since Instruction Count would be the sameCS61C L41 Performance II (7)Garcia © UCBPerformance Calculation (1/2)•CPU execution time for program= Clock Cycles for program x Clock Cycle Time•Substituting for clock cycles: CPU execution time for program= (Instruction Count x CPI) x Clock Cycle Time= Instruction Count x CPI x Clock Cycle TimeCS61C L41 Performance II (8)Garcia © UCBPerformance Calculation (2/2)CPU time = Instructions x Cycles x SecondsProgram Instruction CycleCPU time = Instructions x Cycles x SecondsProgram Instruction CycleCPU time = Instructions x Cycles x SecondsProgram Instruction CycleCPU time = SecondsProgram•Product of all 3 terms: if missing a term, can’t predict time, the real measure of performanceCS61C L41 Performance II (9)Garcia © UCBHow Calculate the 3 Components?•Clock Cycle Time: in specification of computer (Clock Rate in advertisements)•Instruction Count:•Count instructions in loop of small program•Use simulator to count instructions•Hardware counter in spec. register-(Pentium II,III,4)•CPI:•Calculate: Execution Time / Clock cycle timeInstruction Count•Hardware counter in special register (PII,III,4)CS61C L41 Performance II (10)Garcia © UCBCalculating CPI Another Way•First calculate CPI for each individual instruction (add, sub, and, etc.)•Next calculate frequency of each individual instruction•Finally multiply these two for each instruction and add them up to get final CPI (the weighted sum)CS61C L41 Performance II (11)Garcia © UCBExample (RISC processor)Op Freqi CPIi Prod (% Time)ALU 50% 1 .5 (23%)Load 20% 5 1.0 (45%)Store 10% 3 .3 (14%)Branch 20% 2 .4 (18%) 2.2• What if Branch instructions twice as fast?Instruction Mix (Where time spent)CS61C L41 Performance II (12)Garcia © UCBWhat Programs Measure for Comparison?•Ideally run typical programs with typical input before purchase, or before even build machine•Called a “workload”; For example: •Engineer uses compiler, spreadsheet•Author uses word processor, drawing program, compression software•In some situations its hard to do•Don’t have access to machine to “benchmark” before purchase•Don’t know workload in future•Next: benchmarks & PC-Mac showdown!CS61C L41 Performance II (13)Garcia © UCBBenchmarks•Obviously, apparent speed of processor depends on code used to test it•Need industry standards so that different processors can be fairly compared•Companies exist that create these benchmarks: “typical” code used to evaluate systems•Need to be changed every 2 or 3 years since designers could (and do!) target for these standard benchmarksCS61C L41 Performance II (14)Garcia © UCBExample Standardized Benchmarks (1/2)•Standard Performance Evaluation Corporation (SPEC) SPEC CPU2000•CINT2000 12 integer (gzip, gcc, crafty, perl, ...)•CFP2000 14 floating-point (swim, mesa, art, ...)•All relative to base machine Sun 300MHz 256Mb-RAM Ultra5_10, which gets score of 100•www.spec.org/osg/cpu2000/•They measure-System speed (SPECint2000)-System throughput (SPECint_rate2000)CS61C L41 Performance II (15)Garcia © UCBExample Standardized Benchmarks (2/2)•SPEC•Benchmarks distributed in source code•Members of consortium select workload-30+ companies, 40+ universities•Compiler, machine designers target benchmarks,
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