multitime

Overview

Unix's time utility is a simple and often effective way of measuring how long a command takes to run (wall time). Unfortunately, running a command once can give misleading timings: the process may create a cache on its first execution, running faster subsequently; other processes may cause the command to be starved of CPU or IO time; etc. It is common to see people run time several times and take whichever values they feel most comfortable with. Inevitably, this causes problems.

multitime is, in essence, a simple extension to time which runs a command multiple times and prints the timing means, standard deviations, mins, medians, and maxes having done so. This can give a much better understanding of the command's performance.

$ multitime -n 5 awk "function fib(n) \
  { return n <= 1 ? 1 : fib(n - 1) + fib(n - 2) } BEGIN { fib(30) }"
===> multitime results
1: awk "function fib(n) \
  { return n <= 1 ? 1 : fib(n - 1) + fib(n - 2) } BEGIN { fib(30) }"
            Mean        Std.Dev.    Min         Median      Max
real        0.603       0.006       0.599       0.600       0.615       
user        0.556       0.038       0.490       0.570       0.600       
sys         0.000       0.000       0.000       0.000       0.000 

multitime also allows you to manipulate the stdin and stdout of each execution of a command, allowing fine-grained control of a command. For example, using jot to generate random data, we can compare the performance of sort (lexical sort) and sort -n (numeric sort):

$ multitime -i "jot -r 1000000 1 100000" -q -n 10 sort
===> multitime results
1: sort
            Mean        Std.Dev.    Min         Median      Max
real        0.387       0.012       0.372       0.381       0.407       
user        0.283       0.035       0.220       0.290       0.330       
sys         0.049       0.015       0.020       0.050       0.070       
$ multitime -i "jot -r 1000000 1 100000" -q -n 10 sort -n
===> multitime results
1: sort -n
            Mean        Std.Dev.    Min         Median      Max
real        0.488       0.012       0.473       0.484       0.505       
user        0.384       0.025       0.340       0.390       0.420       
sys         0.072       0.015       0.050       0.070       0.100       

Should you use multitime?

If you want to do any of the following, then multitime is worth considering:

  • You want to run a command several times to understand how its timings naturally vary.
  • You want to run a command several times so that temporary blips in system activity do not distort the timings.
  • You need different executions of a command being timed to have different inputs / outputs.
  • You want to compare the timing of multiple commands (e.g. for benchmarking purposes).

multitime can also be used as a drop-in replacement for the POSiX time command: when invoked as time (e.g. via a symlink), multitime behaves as time. For most users, therefore, multitime can safely replace the time binary, even if you don't make use of its advanced features.

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