Module

Benchmark

Inheritance

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)
    

Classes & Modules

Constants

Name   Description
BENCHMARK_VERSION = "2002-04-25"
CAPTION = Benchmark::Tms::CAPTION The default caption string (heading above the output times).
FMTSTR = Benchmark::Tms::FMTSTR The default format string used to display times. See also Benchmark::Tms#format.

Methods

Instance

Visibility Signature
public benchmark (caption = "", label_width = nil, fmtstr = nil, *labels) {|report| ...}
public bm (label_width = 0, *labels) {|report| ...}
public bmbm (width = 0) {|job| ...}
public measure (label = "") {|| ...}
public realtime () {|| ...}

Instance Method Detail

benchmark(caption = "", label_width = nil, fmtstr = nil, *labels) {|report| ...}

Invokes the block with a Benchmark::Report object, which may be used to collect and report on the results of individual benchmark tests. Reserves label_width leading spaces for labels on each line. Prints caption at the top of the report, and uses fmt to format each line. If the block returns an array of Benchmark::Tms objects, these will be used to format additional lines of output. If label parameters are given, these are used to label these extra lines.

Note: Other methods provide a simpler interface to this one, and are suitable for nearly all benchmarking requirements. See the examples in Benchmark, and the bm and bmbm methods.

Example:

    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

Generates:

                    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)

bm(label_width = 0, *labels) {|report| ...}

A simple interface to the benchmark method, bm is generates sequential reports with labels. The parameters have the same meaning as for benchmark.

    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

Generates:

                    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)

bmbm(width = 0) {|job| ...}

Sometimes benchmark results are skewed because code executed earlier encounters different garbage collection overheads than that run later. bmbm attempts to minimize this effect by running the tests twice, the first time as a rehearsal in order to get the runtime environment stable, the second time for real. GC.start is executed before the start of each of the real timings; the cost of this is not included in the timings. In reality, though, there‘s only so much that bmbm can do, and the results are not guaranteed to be isolated from garbage collection and other effects.

Because bmbm takes two passes through the tests, it can calculate the required label width.

      require 'benchmark'

      array = (1..1000000).map { rand }

      Benchmark.bmbm do |x|
        x.report("sort!") { array.dup.sort! }
        x.report("sort")  { array.dup.sort  }
      end

Generates:

       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)

bmbm yields a Benchmark::Job object and returns an array of Benchmark::Tms objects.

measure(label = "") {|| ...}

Returns the time used to execute the given block as a Benchmark::Tms object.

realtime() {|| ...}

Returns the elapsed real time used to execute the given block.