Ruby Benchmark module: meanings of “user”, “system”, and “real”?
>> Benchmark.bm(7) { |b| b.report('Report:') { s = '' ; 10000.times { s += 'a' } } }
user system total real
Report: 0.150000 0.010000 0.160000 ( 0.156361)
These are the same times that the Unix time command or other typical benchmarking tools would report:
user: the amount of time spent executing userspace code (i.e.: your code),
system: the amount of time spent executing kernel code and
real: the "real" amount of time it took to execute the code (i.e. system + user + time spent waiting for I/O, network, disk, user input, etc.). Also known as "wallclock time".
Also
Why real≠user+sys always
Keep in mind that "real" represents actual elapsed time, while user and sys values represent CPU execution time. As a result, on a multicore system, the user and/or sys time (as well as their sum) can actually exceed the real time. For example, on a java app I'm running for class I get this set of values:
real 1m47.363s
user 2m41.318s
sys 0m4.013s