Module: Benchmark

Defined in:
lib/benchmark.rb,
lib/benchmark/version.rb

Overview

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)
    

Defined Under Namespace

Classes: Job, Report, Tms

Constant Summary collapse

BENCHMARK_VERSION =

:nodoc:

"2002-04-25"
CAPTION =

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

Benchmark::Tms::CAPTION
FORMAT =

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

Benchmark::Tms::FORMAT
VERSION =
"0.2.0"

Class Method Summary collapse

Class Method Details

.benchmark(caption = "", label_width = nil, format = nil, *labels) ⇒ Object

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)

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# File 'lib/benchmark.rb', line 168

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
  print ' '*label_width + caption unless caption.empty?
  report = Report.new(label_width, format)
  results = yield(report)
  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, &blk) ⇒ Object

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)

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# File 'lib/benchmark.rb', line 207

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

.bmbm(width = 0) ⇒ Object

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.


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# File 'lib/benchmark.rb', line 249

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 = "") ⇒ Object

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)

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# File 'lib/benchmark.rb', line 294

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

.realtimeObject

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


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# File 'lib/benchmark.rb', line 309

def realtime # :yield:
  r0 = Process.clock_gettime(Process::CLOCK_MONOTONIC)
  yield
  Process.clock_gettime(Process::CLOCK_MONOTONIC) - r0
end