$ perl5.8.2-threaded -MBenchmark::Thread::Size
Performing each test 10 times
(ref) 10 100
  #   (ref)                                                            
  0    1730 ± 6
  1    2085 ± 6
  2    2374 ± 6
  5    3235 ± 6
 10    4664    
 20    7536 ± 4
 50   16144 ± 2
100   30489 ± 8