Programming Tutorials

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Benchmark module in Ruby

By: Emiley J. in Ruby Tutorials on 2009年03月03日 [フレーム]

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)

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