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

<tt>"a"*1_000_000</tt>:

    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'
    include Benchmark         # we need the CAPTION and FMTSTR constants 

    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)