# Benchmark

Module

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

#### BENCHMARK_VERSION

No documentation available

#### 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

No documentation available
Class 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 `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)```

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)```

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.

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)`

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

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 `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)```

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)```

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.

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)`

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