module Benchmark - benchmark: Ruby Standard Library Documentation

# module 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`:

      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:

      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:

      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:

      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:

      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)

### Constants

CAPTION

  The default caption string (heading above the output times).

FORMAT

  The default format string used to display times. See also `Benchmark::Tms#format`.

VERSION

### Public Class Methods

benchmark(caption = "", label_width = nil, format = nil, *labels) { |report| ... } click to toggle source

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 `format` to format each line. (Note: `caption` must contain a terminating newline character, see the default Benchmark::Tms::CAPTION for an example.)

Returns an array of `Benchmark::Tms` objects.

If the block returns an array of `Benchmark::Tms` objects, these will be used to format additional lines of output. If `labels` parameter 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 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

Generates:

                  user     system      total        real
    for:      0.970000   0.000000   0.970000 (  0.970493)
    times:    0.990000   0.000000   0.990000 (  0.989542)
    upto:     0.970000   0.000000   0.970000 (  0.972854)
    >total:   2.930000   0.000000   2.930000 (  2.932889)
    >avg:     0.976667   0.000000   0.976667 (  0.977630)

    # File benchmark.rb, line 170
    def benchmark(caption = "", label_width = nil, format = nil, *labels) # :yield: report
      sync = $stdout.sync
      $stdout.sync = true
      label_width ||= 0
      label_width += 1
      format ||= FORMAT
      report = Report.new(label_width, format)
      results = yield(report)

      print " " * report.width + caption unless caption.empty?
      report.list.each { |i|
        print i.label.to_s.ljust(report.width)
        print i.format(report.format, *format)
      }

      Array === results and results.grep(Tms).each {|t|
        print((labels.shift || t.label || "").ljust(label_width), t.format(format))
      }
      report.list
    ensure
      $stdout.sync = sync unless sync.nil?
    end

bm(label_width = 0, *labels) { |report| ... } click to toggle source

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

    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

Generates:

                  user     system      total        real
    for:      0.960000   0.000000   0.960000 (  0.957966)
    times:    0.960000   0.000000   0.960000 (  0.960423)
    upto:     0.950000   0.000000   0.950000 (  0.954864)

    # File benchmark.rb, line 215
    def bm(label_width = 0, *labels, &blk) # :yield: report
      benchmark(CAPTION, label_width, FORMAT, *labels, &blk)
    end

bmbm(width = 0) { |job| ... } click to toggle source

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!   1.440000   0.010000   1.450000 (  1.446833)
    sort    1.440000   0.000000   1.440000 (  1.448257)
    -------------------------------- total: 2.890000sec

                user     system      total        real
    sort!   1.460000   0.000000   1.460000 (  1.458065)
    sort    1.450000   0.000000   1.450000 (  1.455963)

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

    # File benchmark.rb, line 257
    def bmbm(width = 0) # :yield: job
      job = Job.new(width)
      yield(job)
      width = job.width + 1
      sync = $stdout.sync
      $stdout.sync = true

      # rehearsal
      puts 'Rehearsal '.ljust(width+CAPTION.length,'-')
      ets = job.list.inject(Tms.new) { |sum,(label,item)|
        print label.ljust(width)
        res = Benchmark.measure(&item)
        print res.format
        sum + res
      }.format("total: %tsec")
      print " #{ets}\n\n".rjust(width+CAPTION.length+2,'-')

      # take
      print ' '*width + CAPTION
      job.list.map { |label,item|
        GC.start
        print label.ljust(width)
        Benchmark.measure(label, &item).tap { |res| print res }
      }
    ensure
      $stdout.sync = sync unless sync.nil?
    end

measure(label = "") { || ... } click to toggle source

Returns the time used to execute the given block as a `Benchmark::Tms` object. Takes `label` option.

    require 'benchmark'

    n = 1000000

    time = Benchmark.measure do
      n.times { a = "1" }
    end
    puts time

Generates:

    0.220000   0.000000   0.220000 (  0.227313)

    # File benchmark.rb, line 302
    def measure(label = "") # :yield:
      t0, r0 = Process.times, Process.clock_gettime(Process::CLOCK_MONOTONIC)
      yield
      t1, r1 = Process.times, Process.clock_gettime(Process::CLOCK_MONOTONIC)
      Benchmark::Tms.new(t1.utime  - t0.utime,
                         t1.stime  - t0.stime,
                         t1.cutime - t0.cutime,
                         t1.cstime - t0.cstime,
                         r1 - r0,
                         label)
    end

realtime() { || ... } click to toggle source

Returns the elapsed real time used to execute the given block. The unit of time is seconds.

    Benchmark.realtime { "a" * 1_000_000_000 }
    #=> 0.5098029999935534

    # File benchmark.rb, line 321
    def realtime # :yield:
      r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
      yield
      Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
    end

### Private Instance Methods

benchmark(caption = "", label_width = nil, format = nil, *labels) { |report| ... } click to toggle source

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 `format` to format each line. (Note: `caption` must contain a terminating newline character, see the default Benchmark::Tms::CAPTION for an example.)

Returns an array of `Benchmark::Tms` objects.

If the block returns an array of `Benchmark::Tms` objects, these will be used to format additional lines of output. If `labels` parameter 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 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

Generates:

                  user     system      total        real
    for:      0.970000   0.000000   0.970000 (  0.970493)
    times:    0.990000   0.000000   0.990000 (  0.989542)
    upto:     0.970000   0.000000   0.970000 (  0.972854)
    >total:   2.930000   0.000000   2.930000 (  2.932889)
    >avg:     0.976667   0.000000   0.976667 (  0.977630)

    # File benchmark.rb, line 170
    def benchmark(caption = "", label_width = nil, format = nil, *labels) # :yield: report
      sync = $stdout.sync
      $stdout.sync = true
      label_width ||= 0
      label_width += 1
      format ||= FORMAT
      report = Report.new(label_width, format)
      results = yield(report)

      print " " * report.width + caption unless caption.empty?
      report.list.each { |i|
        print i.label.to_s.ljust(report.width)
        print i.format(report.format, *format)
      }

      Array === results and results.grep(Tms).each {|t|
        print((labels.shift || t.label || "").ljust(label_width), t.format(format))
      }
      report.list
    ensure
      $stdout.sync = sync unless sync.nil?
    end

bm(label_width = 0, *labels) { |report| ... } click to toggle source

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

    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

Generates:

                  user     system      total        real
    for:      0.960000   0.000000   0.960000 (  0.957966)
    times:    0.960000   0.000000   0.960000 (  0.960423)
    upto:     0.950000   0.000000   0.950000 (  0.954864)

    # File benchmark.rb, line 215
    def bm(label_width = 0, *labels, &blk) # :yield: report
      benchmark(CAPTION, label_width, FORMAT, *labels, &blk)
    end

bmbm(width = 0) { |job| ... } click to toggle source

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!   1.440000   0.010000   1.450000 (  1.446833)
    sort    1.440000   0.000000   1.440000 (  1.448257)
    -------------------------------- total: 2.890000sec

                user     system      total        real
    sort!   1.460000   0.000000   1.460000 (  1.458065)
    sort    1.450000   0.000000   1.450000 (  1.455963)

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

    # File benchmark.rb, line 257
    def bmbm(width = 0) # :yield: job
      job = Job.new(width)
      yield(job)
      width = job.width + 1
      sync = $stdout.sync
      $stdout.sync = true

      # rehearsal
      puts 'Rehearsal '.ljust(width+CAPTION.length,'-')
      ets = job.list.inject(Tms.new) { |sum,(label,item)|
        print label.ljust(width)
        res = Benchmark.measure(&item)
        print res.format
        sum + res
      }.format("total: %tsec")
      print " #{ets}\n\n".rjust(width+CAPTION.length+2,'-')

      # take
      print ' '*width + CAPTION
      job.list.map { |label,item|
        GC.start
        print label.ljust(width)
        Benchmark.measure(label, &item).tap { |res| print res }
      }
    ensure
      $stdout.sync = sync unless sync.nil?
    end

measure(label = "") { || ... } click to toggle source

Returns the time used to execute the given block as a `Benchmark::Tms` object. Takes `label` option.

    require 'benchmark'

    n = 1000000

    time = Benchmark.measure do
      n.times { a = "1" }
    end
    puts time

Generates:

    0.220000   0.000000   0.220000 (  0.227313)

    # File benchmark.rb, line 302
    def measure(label = "") # :yield:
      t0, r0 = Process.times, Process.clock_gettime(Process::CLOCK_MONOTONIC)
      yield
      t1, r1 = Process.times, Process.clock_gettime(Process::CLOCK_MONOTONIC)
      Benchmark::Tms.new(t1.utime  - t0.utime,
                         t1.stime  - t0.stime,
                         t1.cutime - t0.cutime,
                         t1.cstime - t0.cstime,
                         r1 - r0,
                         label)
    end

realtime() { || ... } click to toggle source

Returns the elapsed real time used to execute the given block. The unit of time is seconds.

    Benchmark.realtime { "a" * 1_000_000_000 }
    #=> 0.5098029999935534

    # File benchmark.rb, line 321
    def realtime # :yield:
      r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
      yield
      Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
    end