Module Benchmark
In: lib/benchmark.rb

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)
    

Methods

benchmark   bm   bmbm   measure   realtime  

Classes and Modules

Class Benchmark::Tms

Constants

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.

Public Instance methods

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)

[Source]

# File lib/benchmark.rb, line 170
  def benchmark(caption = "", label_width = nil, fmtstr = nil, *labels) # :yield: report
    sync = STDOUT.sync
    STDOUT.sync = true
    label_width ||= 0
    fmtstr ||= FMTSTR
    raise ArgumentError, "no block" unless iterator?
    print caption
    results = yield(Report.new(label_width, fmtstr))
    Array === results and results.grep(Tms).each {|t|
      print((labels.shift || t.label || "").ljust(label_width), 
            t.format(fmtstr))
    }
    STDOUT.sync = sync
  end

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)

[Source]

# File lib/benchmark.rb, line 206
  def bm(label_width = 0, *labels, &blk) # :yield: report
    benchmark(" "*label_width + CAPTION, label_width, FMTSTR, *labels, &blk)
  end

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.

[Source]

# File lib/benchmark.rb, line 248
  def bmbm(width = 0, &blk) # :yield: job
    job = Job.new(width)
    yield(job)
    width = job.width
    sync = STDOUT.sync
    STDOUT.sync = true

    # rehearsal
    print "Rehearsal "
    puts '-'*(width+CAPTION.length - "Rehearsal ".length)
    list = []
    job.list.each{|label,item|
      print(label.ljust(width))
      res = Benchmark::measure(&item)
      print res.format()
      list.push res
    }
    sum = Tms.new; list.each{|i| sum += i}
    ets = sum.format("total: %tsec")
    printf("%s %s\n\n",
           "-"*(width+CAPTION.length-ets.length-1), ets)
    
    # take
    print ' '*width, CAPTION
    list = []
    ary = []
    job.list.each{|label,item|
      GC::start
      print label.ljust(width)
      res = Benchmark::measure(&item)
      print res.format()
      ary.push res
      list.push [label, res]
    }

    STDOUT.sync = sync
    ary
  end

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

[Source]

# File lib/benchmark.rb, line 291
  def measure(label = "") # :yield:
    t0, r0 = Benchmark.times, Time.now
    yield
    t1, r1 = Benchmark.times, Time.now
    Benchmark::Tms.new(t1.utime  - t0.utime, 
                       t1.stime  - t0.stime, 
                       t1.cutime - t0.cutime, 
                       t1.cstime - t0.cstime, 
                       r1.to_f - r0.to_f,
                       label)
  end

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

[Source]

# File lib/benchmark.rb, line 306
  def realtime(&blk) # :yield:
    r0 = Time.now
    yield
    r1 = Time.now
    r1.to_f - r0.to_f
  end

[Validate]