gistfile1.rb

require 'benchmark'

TIMES = 10_000_000

module M
  X = ''
  module N
    module A
      module B
        def self.x
          X
        end
      end
    end
  end
end

Benchmark.bm do |x|
  x.report("constant") { TIMES.times { ::M::N::A::B.x }}
  x.report("literal") { TIMES.times { '' }}
  x.report("frozen") { TIMES.times { ''.freeze }}
end

__END__
[aaron@higgins git]$ ruby gistfile1.rb 
       user     system      total        real
constant  0.890000   0.000000   0.890000 (  0.892681)
literal  1.200000   0.000000   1.200000 (  1.202642)
frozen  0.520000   0.000000   0.520000 (  0.516941)
[aaron@higgins git]$