From: Charles Oliver Nutter <charles.nutter@...>
Date: 2007-12-22T23:42:03+09:00
Subject: Re: Experimental PATCH to improve thread performance

Brent Roman wrote:
> 
> Charles Oliver Nutter-2 wrote:
>>
>> I'd love to know what broke in JRuby. I tried both benchmarks and 
>> they're very snappy on my machine. We're making a big push to get JRuby 
>> threading solid, so please let us know what you've seen.
>>
>>
> 
> I'd like to work with you on this after the holidays.
> In the meantime, I've attached a java backtrace
> of the failure in our dreaded "killer app"
> Let me know if you can glean anything from it that will
> help me create a simple test case for you.
> 
> http://www.nabble.com/file/p14467248/jruby-1.1b1.backtrace
> jruby-1.1b1.backtrace 
> 
> By the way,
> The benchmark numbers I see here are very consistent with your claim
> that JRuby is faster than Ruby 1.8.6.  In this case, it's a lot faster:
> 
>                Unpatched 1.8.6    Patched 1.8.6   JRuby 1.1b1      Ruby 1.9
> Bench #1  22sec / 16 MB       4sec  / 7 MB     3.5sec / 21 MB    0.06sec
> Bench #2  35sec / 10 MB      15sec  / 7 MB    2.8sec / 17 MB    0.36sec
> 
> I realize that these numbers penalize JRuby for its JVM start up delay,
> but, even so, it's clear that when Ruby 1.9 is finally ready, 
> it will be the horse to beat ;-)

Oh, one other feature of JRuby might be interesting here, and 
interesting for Ruby 1.9, so I'm not totally OT).

JRuby uses native threads, as you know. This increases the cost of 
spinning up many threads, since green threads are much cheaper. So in 
JRuby, I implemented an optional thread-pooling mode that uses Java's 
concurrency APIs. In this mode, threads are reused; the number of native 
threads used is only as high as the total number of threads running 
concurrently, and those threads get reused until they age out of the pool:

CODE:
t = Time.now; 100000.times { Thread.new {} }; p Time.now - t

JRuby unpooled:
26.045

JRuby pooled: (-J-Djruby.thread.pooling=true)
3.572

Ruby 1.8.6:
0.537061

Ruby 1.9:
13.925661

(Note this doesn't test the time required for all threads to 
complete...just to construct them)

JRuby's not quite as fast as MRI here, but that's mostly because we 
construct many more runtime structures per thread (like preallocating a 
frame stack 50 deep to safe the cost of allocating later) and I think we 
can probably approach MRI thread-spawning performance with a little 
work. For now, it's good enough.

I would expect this same technique would apply well to Ruby 1.9, and 
probably give similar performance gains. I'd be happy to describe it if 
anyone's interested.

- Charlie