Programming Tutorials

Benchmark module in Ruby

By: Emiley J. in Ruby Tutorials on 2009-03-03  

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:

      require 'benchmark'
  
      puts Benchmark.measure { "a"*1_000_000 }
  

  On my machine (FreeBSD 3.2 on P5, 100MHz) this generates:

      1.166667   0.050000   1.216667 (  0.571355)
  

  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:

      require 'benchmark'
  
      n = 50000
      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
         1.033333   0.016667   1.016667 (  0.492106)
         1.483333   0.000000   1.483333 (  0.694605)
         1.516667   0.000000   1.516667 (  0.711077)
  

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

      require 'benchmark'
  
      n = 50000
      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:     1.050000   0.000000   1.050000 (  0.503462)
       times:   1.533333   0.016667   1.550000 (  0.735473)
       upto:    1.500000   0.016667   1.516667 (  0.711239)

• 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:

      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!  11.928000   0.010000  11.938000 ( 12.756000)
       sort   13.048000   0.020000  13.068000 ( 13.857000)
       ------------------------------- total: 25.006000sec
  
                   user     system      total        real
       sort!  12.959000   0.010000  12.969000 ( 13.793000)
       sort   12.007000   0.000000  12.007000 ( 12.791000)
  

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

      require 'benchmark'
  
      n = 50000
      Benchmark.benchmark(" "*7 + CAPTION, 7, FMTSTR, ">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:     1.016667   0.016667   1.033333 (  0.485749)
       times:   1.450000   0.016667   1.466667 (  0.681367)
       upto:    1.533333   0.000000   1.533333 (  0.722166)
       >total:  4.000000   0.033333   4.033333 (  1.889282)
       >avg:    1.333333   0.011111   1.344444 (  0.629761)