Module: Benchmark

Module | Benchmark
In: | 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

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)

[Source]

    # File 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

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)

[Source]

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

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.

[Source]

    # File 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

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

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

[Source]

    # File 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

realtime() {|| ...}

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

[Source]

    # File benchmark.rb, line 306
      def realtime(&blk) # :yield:
        Benchmark::measure(&blk).real
      end

[Validate]