From: Eric Hodel <drbrain@...7.net>
Date: 2013-03-04T13:59:29+09:00
Subject: Re: ruby 2.0 slower than 1.9.3 ?


On Mar 3, 2013, at 14:04, Bug Free <lists@ruby-forum.com> wrote:

> I'm running a simple CPU intensive benchmark:
> 
> puts (0..11).to_a.permutation.inject(0) { |m, _| m += 1 }
> 
> This takes around 158s with 1.9.3 and 200s with 2.0. Any thoughts on how
> I can get performance back ?

I suggest you file a bug on http://bugs.ruby-lang.org.  I also see the performance drop, about 8%.

I profiled a smaller benchmark: 

$ ruby19 -v -rprofile -e '(0..7).to_a.permutation.inject(0) { |m, _| m += 1 }'
ruby 1.9.3p374 (2013-01-15 revision 38858) [x86_64-darwin12.2.1]
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 75.00     0.27      0.27        2   135.00   180.00  Array#permutation
 25.00     0.36      0.09    40320     0.00     0.00  Fixnum#+
  0.00     0.36      0.00        1     0.00     0.00  Range#each
  0.00     0.36      0.00        1     0.00     0.00  Enumerable.to_a
  0.00     0.36      0.00        1     0.00   360.00  Enumerator#each
  0.00     0.36      0.00        1     0.00   360.00  Enumerable.inject
  0.00     0.36      0.00        1     0.00   360.00  #toplevel

I'm unsure what this "nil#" method ruby 2 records is, or if it is only an artifact of TracePoint.  It's also worth a bug report.

$ ruby -v -rprofile -e '(0..7).to_a.permutation.inject(0) { |m, _| m += 1 }'
ruby 2.0.0p0 (2013-02-24 revision 39473) [x86_64-darwin12.2.1]
  %   cumulative   self              self     total
 time   seconds   seconds    calls  ms/call  ms/call  name
 52.31     0.34      0.34    40320     0.01     0.01  nil#
 35.38     0.57      0.23        2   115.00   325.00  Array#permutation
 12.31     0.65      0.08    40320     0.00     0.00  Fixnum#+
  0.00     0.65      0.00        1     0.00     0.00  TracePoint#enable
  0.00     0.65      0.00        1     0.00     0.00  Enumerable#to_a
  0.00     0.65      0.00        1     0.00     0.00  Range#each
  0.00     0.65      0.00        1     0.00   650.00  Enumerator#each
  0.00     0.65      0.00        1     0.00   650.00  Enumerable#inject
  0.00     0.65      0.00        1     0.00     0.00  TracePoint#disable
  0.00     0.65      0.00        1     0.00   650.00  #toplevel