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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.

Public Class Methods

benchmark(caption = "", label_width = nil, format = nil, *labels) 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. 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 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 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 164
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) click to toggle source

A simple interface to the benchmark method, bm generates sequential reports with labels. The 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 203
def bm(label_width = 0, *labels, &blk) # :yield: report
  benchmark(CAPTION, label_width, FORMAT, *labels, &blk)
end
            
bmbm(width = 0) 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 245
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.

 
               # File benchmark.rb, line 277
def measure(label = "") # :yield:
  t0, r0 = Process.times, Time.now
  yield
  t1, r1 = Process.times, Time.now
  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.

 
               # File benchmark.rb, line 292
def realtime # :yield:
  r0 = Time.now
  yield
  Time.now - r0
end
            

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