Benchmark

The Benchmark module provides methods to measure and report the time used to execute Ruby code.

• Measure the time to construct the string given by the expression "a"*1_000_000_000:

  Example

  Run in Playground

  require 'benchmark'
  
  puts Benchmark.measure { "a"*1_000_000_000 }
  

  On my machine (OSX 10.8.3 on i5 1.7 GHz) this generates:

  0.350000   0.400000   0.750000 (  0.835234)

  This report shows the user CPU time, system CPU time, the sum of the user and system CPU times, and the elapsed real time. The unit of time is seconds.

• Do some experiments sequentially using the bm method:

  Example

  Run in Playground

  require 'benchmark'
  
  n = 5000000
  Benchmark.bm do |x|
    x.report { for i in 1..n; a = "1"; end }
    x.report { n.times do   ; a = "1"; end }
    x.report { 1.upto(n) do ; a = "1"; end }
  end
  

  The result:

      user     system      total        real
  1.010000   0.000000   1.010000 (  1.014479)
  1.000000   0.000000   1.000000 (  0.998261)
  0.980000   0.000000   0.980000 (  0.981335)

• Continuing the previous example, put a label in each report:

  Example

  Run in Playground

  require 'benchmark'
  
  n = 5000000
  Benchmark.bm(7) do |x|
    x.report("for:")   { for i in 1..n; a = "1"; end }
    x.report("times:") { n.times do   ; a = "1"; end }
    x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
  end
  

The result:

              user     system      total        real
for:      1.010000   0.000000   1.010000 (  1.015688)
times:    1.000000   0.000000   1.000000 (  1.003611)
upto:     1.030000   0.000000   1.030000 (  1.028098)

• The times for some benchmarks depend on the order in which items are run. These differences are due to the cost of memory allocation and garbage collection. To avoid these discrepancies, the bmbm method is provided. For example, to compare ways to sort an array of floats:

  Example

  Run in Playground

  require 'benchmark'
  
  array = (1..1000000).map { rand }
  
  Benchmark.bmbm do |x|
    x.report("sort!") { array.dup.sort! }
    x.report("sort")  { array.dup.sort  }
  end
  

  The result:

  Rehearsal -----------------------------------------
  sort!   1.490000   0.010000   1.500000 (  1.490520)
  sort    1.460000   0.000000   1.460000 (  1.463025)
  -------------------------------- total: 2.960000sec
  
              user     system      total        real
  sort!   1.460000   0.000000   1.460000 (  1.460465)
  sort    1.450000   0.010000   1.460000 (  1.448327)

• Report statistics of sequential experiments with unique labels, using the benchmark method:

  Example

  Run in Playground

  require 'benchmark'
  include Benchmark         # we need the CAPTION and FORMAT constants
  
  n = 5000000
  Benchmark.benchmark(CAPTION, 7, FORMAT, ">total:", ">avg:") do |x|
    tf = x.report("for:")   { for i in 1..n; a = "1"; end }
    tt = x.report("times:") { n.times do   ; a = "1"; end }
    tu = x.report("upto:")  { 1.upto(n) do ; a = "1"; end }
    [tf+tt+tu, (tf+tt+tu)/3]
  end
  

  The result:

               user     system      total        real
  for:      0.950000   0.000000   0.950000 (  0.952039)
  times:    0.980000   0.000000   0.980000 (  0.984938)
  upto:     0.950000   0.000000   0.950000 (  0.946787)
  >total:   2.880000   0.000000   2.880000 (  2.883764)
  >avg:     0.960000   0.000000   0.960000 (  0.961255)