From: Charles Oliver Nutter <charles.nutter@...>
Date: 2007-11-01T13:13:29+09:00
Subject: Re: JRuby perf questions answered

Roger Pack wrote:
>> any questions?
> 
> Startup time and comparison with 1.9? :)

Startup time varies widely between platforms. OS X is probably one of 
the fastest:

~/NetBeansProjects/jruby $ time ruby -e "puts 'hello'"
hello

real    0m0.015s
user    0m0.007s
sys     0m0.008s
~/NetBeansProjects/jruby $ time jruby -e "puts 'hello'"
hello

real    0m1.815s
user    0m1.709s
sys     0m0.183s

There's been reports that on server-class machines the startup time can 
be as high as 5-10 seconds. The slow startup time is partially due to 
the JVM and partially our fault (JRuby's complicated, yo).

As for Ruby 1.9...it's hard to make a comparison right now. Most of the 
benchmarks we use to measure Ruby 1.9 (like those I described 
previously) are usually a bit faster in Ruby 1.9. And of course almost 
all of Ruby 1.9's benchmarks are fastest in Ruby 1.9.

Part of the difficulty comparing is that Ruby 1.9 contains a bunch of 
changes to Ruby language semantics that we have not yet put in JRuby, 
since we've focused on 1.8 compatibility. Things like:

- fast math operations, that speed up +, -, etc, but you can't override them
- constant-time case/when when literal values are used, but you can't 
override === for those literal types

Here's A few numbers, for your edification. Some things are faster in 
Ruby 1.9:

JRuby:
~/NetBeansProjects/jruby $ jruby -J-server 
test/bench/bench_fib_recursive.rb
   0.869000   0.000000   0.869000 (  0.869000)
   0.677000   0.000000   0.677000 (  0.677000)
   0.652000   0.000000   0.652000 (  0.652000)
   0.648000   0.000000   0.648000 (  0.648000)

Ruby 1.9:
~/NetBeansProjects/jruby $ ../ruby1.9/ruby -I ../ruby1.9/lib 
test/bench/bench_fib_recursive.rb
   0.400000   0.000000   0.400000 (  0.405639)
   0.400000   0.000000   0.400000 (  0.406707)
   0.400000   0.000000   0.400000 (  0.400150)
   0.400000   0.000000   0.400000 (  0.398065)

And some things are slower:

JRuby:
1m loops yielding three fixnums 10 times to block splatting and 
accessing them
   3.387000   0.000000   3.387000 (  3.387000)
   3.314000   0.000000   3.314000 (  3.315000)
   3.235000   0.000000   3.235000 (  3.235000)

Ruby 1.9:
1m loops yielding three fixnums 10 times to block splatting and 
accessing them
   4.980000   0.020000   5.000000 (  5.055369)
   4.980000   0.020000   5.000000 (  5.073821)
   5.010000   0.020000   5.030000 (  5.088681)

And so on. However, for Rails, I've only seen one comparison that showed 
Ruby 1.9 was either slightly faster or slower than Ruby 1.8.x:

http://eigenclass.org/hiki/non-synthetic-benchmarks-for-yarv

I'm not sure if there's been a more recent comparison. I believe we'll 
be able to match Ruby 1.9 performance once we start making the same 
optimizations.

- Charlie