Hello everyone,


What is the convenient way to calculate the execution time of a function? The function may be not a long and time consuming function -- only 10 lines in some situation.


thanks in advance,
George

does the 'time' command help?

There are 3 times to consider:
1- The system times: the time spent by the kernel on behalf the process, that is: servicing system calls, doing thread related computations too in systems with native threads, page faults and so on.

2- The CPU times: the effective time spent by the process in the CPU. This is independent from system load.

3- The clock time: the total time spent from start to finish (what the user would notice anyway). It isn't precise as it depends on system load.

To get them you may use the getrusage() system call for #1 & #2 and gettimeofday() for #3, or times() to get them all. I prefer getrusage()/gettimeofday() because it has microsecond resolution.


PS: Depending on what you are trying to measure, you may use the sum of #1 and #2. Use #2 when you want to measure computations and #1 to measure system call overhead.

PS: Also, you may get rusage information for each child using wait3()/wait4()

time is useful cmd, but you can get more info from the GNU version '\time':

[ ~]$ time ./t.pl
undeff

real 0m0.210s
user 0m0.116s
sys 0m0.016s
[ ~]$ \time ./t.pl
undeff
0.11user 0.00system 0:00.13elapsed 95%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+1357minor)pagefaults 0swaps

If you more precise time information (time spent in each function), have a look at "gprof".