Computer Abstractions and Technology: Performance II Lecture Notes PDF

Computer Abstractions and Technology : Performance II 471029: Introduction to Computer Architecture 4th Lecture Disclaimer: Slides are mainly based on COD 5th textbook and also developed in part by Profs. Dohyung Kim @ KNU and Computer architecture course @ KAIST and SKKU...

Computer Abstractions and Technology : Performance II 471029: Introduction to Computer Architecture 4th Lecture Disclaimer: Slides are mainly based on COD 5th textbook and also developed in part by Profs. Dohyung Kim @ KNU and Computer architecture course @ KAIST and SKKU 1 Execution time  Three are different types of time  Elapsed time (aka wall-clock time)  Based on realtime clock (coutiguously running)  Includes time spent in all other activities  CPU time (aka virtual process time)  Time when process is executing (CPU is active) user time and system time (can mean different things)   Does not include time when process is inherently waiting  Parallel execution time  Multi-core & Multi-thread execution environment  Runs whenever any parallel part is executing  Need to define a global time bases  We’ll talk about it later 2 How can we measure execution time for a specific program? or task? 3 Timer: gettimeofday()  UNIX function  Returns wall-clock time in seconds and microseconds  Actual resolution is hardware-dependent  Base value is 00:00 UTC, January 1, 1970  Some implementations also return the timezone #include struct timeval tv; double walltime; gettimeofday(&tv, NULL); walltime = tv.tv_sec + tv.tv_usec * 1.0e-6; 4 Timer: clock_gettime()  POSIX function  For clock_id CLOCK_REALTIME returns wall-clock time in seconds and nanoseconds  More clocks may be implemented but are not standardized  Actual resolution is hardware-dependent #include struct timespec tv; double walltime; Clock_gettime(CLOCK_REALTIME, &tv); walltime = tv.tv_sec + tv.tv_nsec * 1.0e-9; 5 Timer: getrusage()  UNIX function  Provides a variety of different information  Including user time, system time, memory usage, page faults, etc.  Information provided system-dependent! #include struct rusage ru; double usrtime; int memused; getrusage(RUSAGE_SELF, &ru); usrtime = ru.ru_utime.tv_sec + ru.ru_utime.tv_usec * 1.0e-6; memused = ru.ru_maxrss; 6 Timer: TSC(Time Stamp Counter)  H/W counter  Count the clock cycle (or tick)  RDTSC instructions on x86 (return in EDX:EAX) #include #include uint32_t tickl, tickh; asm volatile (“rdtsc”: “=a”(tickl), “=d”(tickh)); // ((uint64_t)tickh