问题
Right now, I'm trying to determine a method to measure the time that a particular function will take (something like pthread_create). Now, of course, these types of functions are extremely optimized to take as little time as possible; so little, in fact, that my timer that uses gettimeofday in userspace which measures in microseconds is unable to adequately measure anything.
Normally, if I could mess with the kernel, I'd use something like get_cycles to measure the raw number of cycles as a performance metric. However, I haven't found a way to do this in userspace. Is there a way to use get_cycles (or an equivalent) or some other higher precision timer I could use in userspace to measure extremely fast functions?
回答1:
clock_gettime allows you to get a nanosecond-precise time from the thread start, process start or epoch.
回答2:
Use RDTSC (if you're on x86), or clock_gettime
unsigned long long cycleCount() {
asm ("rdtsc");
}
回答3:
Have you tried getting the time it takes to execute your function, say, 10000 times and taking the mean? That would save the bother of finding more accurate timing functions.
Having said that, this answer: Is gettimeofday() guaranteed to be of microsecond resolution? seems to indicate better functions to use than gettimeofday().
回答4:
My linux man page tells me
CONFORMING TO
SVr4, 4.3BSD. POSIX.1-2001 describes gettimeofday() but not settimeofday(). POSIX.1-2008 marks gettimeofday() as obsolete, recomending the use of clock_gettime(2) instead.
来源：https://stackoverflow.com/questions/5165108/high-precision-timing-in-userspace-in-linux