Source of Ruby benchmark irregularites

Question

Running this code:

require 'benchmark'

Benchmark.bm do |x|
  x.report("1+1") {15_000_000.times {1+1}}
  x.report("1+1") {15_000_000.times {1+1}}
  x.report("1+1") {15_000_000.times {1+1}}
  x.report("1+1") {15_000_000.times {1+1}}
  x.report("1+1") {15_000_000.times {1+1}}
end

Outputs these results:

       user     system      total        real
1+1  2.188000   0.000000   2.188000 (  2.250000)
1+1  2.250000   0.000000   2.250000 (  2.265625)
1+1  2.234000   0.000000   2.234000 (  2.250000)
1+1  2.203000   0.000000   2.203000 (  2.250000)
1+1  2.266000   0.000000   2.266000 (  2.281250)

Guessing the variation is a result of the system environment, but wanted to confirm this is the case.

Answer 1

"Guessing the variation is a result of the system environment", you are right.

Benchmarks can't be precise all time. You don't have a perfect regular machine to run something always in the same time. Take two numbers from benchmark as the same if they were too near, as in this case.