Making Programs Faster

Simple Measurement Tools

Most Unix systems come with a command called time
For quick estimates of entire programs, the time command is handy

        % time ls
        #BIGMESS#       PENN    YAPC_16.jpg     gym     photos
        ...
        real    0m0.858s
        user    0m0.130s
        sys     0m0.230s

Often this is built into the shell; the time program is different:

        % /usr/bin/time ls
        #BIGMESS#       PENN    YAPC_16.jpg     gym     photos
        ...
        0.13user 0.23system 0:00.86elapsed 41%CPU
        (0avgtext+0avgdata 0maxresident)k
        0inputs+0outputs (130major+24minor)pagefaults 0swaps

41%CPU here is the CPU utilization
- It's just CPU time divided by wallclock time
Most of the other information is provided by the getrusage system call
- Not all systems provide all the possible information
- Hence the 0outputs result on my system