From: Charles Oliver Nutter <charles.nutter@...>
Date: 2008-05-13T12:26:48+09:00
Subject: Re: Huge performance gap

Vidar Hokstad wrote:
> On May 12, 7:54 am, Roger Pack <rogerpack2...@gmail.com> wrote:
>> Bill Kelly wrote:
>>> But yes, it's harder to make a language like Ruby, which is highly
>>> dynamic at runtime, fast like C++ and Java, which are primarily
>>> statically compiled.  The Smalltalk folks have reportedly done pretty
>>> well though, so there exists the possiblilty that Ruby may get
>>> substantially faster in the future.  YARV is already making some
>>> headway.
>> My question is what does 1.9 exactly do with its "Inline (Method)
>> cache"[1]?  Is there room for more improvement with a better JIT
>> compiler?  How much would this help scripts?
> 
> There's a huge amount of room for improvement in the still. I haven't
> seen any of the Ruby implementations even try to apply more
> sophisticated
> VM/JIT techniques such as tracing and polymorphic inline caches
> properly.

I've experimented with PICs in JRuby, and for most tests I ran they did 
not help very much. Granted, there's an unfortunate lack of nontrivial 
polymorphic benchmarks in the wild, so it's possible a good PIC would 
help more on real apps.

What does make a huge difference for JRuby is eliminating some of the 
extra overhead related to rarely-used Ruby features. For example, the 
difference between a normal run and a run that eliminates an unnecessary 
frame object, uses fast dispatch for math operations, and eliminates 
some thread checkpointing:

~/NetBeansProjects/jruby ➔ jruby -J-server 
test/bench/bench_fib_recursive.rb
   0.746000   0.000000   0.746000 (  0.746000)
   0.371000   0.000000   0.371000 (  0.370000)
   0.357000   0.000000   0.357000 (  0.357000)
   0.357000   0.000000   0.357000 (  0.357000)
   0.358000   0.000000   0.358000 (  0.357000)
~/NetBeansProjects/jruby ➔ jruby -J-server 
-J-Djruby.compile.fastest=true test/bench/bench_fib_recursive.rb
   0.960000   0.000000   0.960000 (  0.959000)
   0.243000   0.000000   0.243000 (  0.243000)
   0.238000   0.000000   0.238000 (  0.238000)
   0.237000   0.000000   0.237000 (  0.237000)
   0.235000   0.000000   0.235000 (  0.235000)

And Ruby 1.9:

~/NetBeansProjects/jruby ➔ ../ruby1.9/ruby -I ../ruby1.9/lib 
test/bench/bench_fib_recursive.rb
   0.400000   0.010000   0.410000 (  0.412421)
   0.400000   0.000000   0.400000 (  0.407236)
   0.400000   0.000000   0.400000 (  0.415222)
   0.400000   0.010000   0.410000 (  0.417042)
   0.400000   0.000000   0.400000 (  0.452934)

So yes, there's definitely room to improve all the implementations...

- Charlie