Re: Ruby performance improvements

Michael Selig wrote:
> ----- Original Message -----
> From: "Charles Oliver Nutter" <[e-mail]>
> 
> 
>>> 2) Loops & rb_yield()
>>> Most of Ruby's loops end up calling rb_yield() for each iteration.
> However
>>> much of the work that rb_yield_0 does each time can be often be done
> once at
>>> the start of the loop:
>>>     - Pushing frame, block, vars, class etc
>>>     - Freeing/creation of dynamic variables (instead they can be
> initialized
>>> to NIL each time, unless the context has been saved)
>>> Also loops done by rb_iterate() (via an IFUNC stub) can be simplified
>>> further to reduce the overhead of "double-yield".
>> This one I haven't tried, but it's a great idea. I could modify the
>> yield logic in our ThreadContext to do loops natively, likely improving
>> the performance of such loops quite a bit. One concern would be making
>> sure the looped block doesn't capture additional scope...you'd
>> negatively effect the resulting capture
> The code I wrote checks for this, and if the scope has been captured, it
> allocates a new dynamic block. Luckily it was very simple to implement, as
> ruby sets a flag DVAR_DONT_RECYCLE when the scope is captured.

Interesting...we could probably do the same in JRuby to reduce the 
overhead of repeat block invocations.

> One other thing that I think is worth doing is to make variables created in
> a block into "local" variables rather than "dynamic" if possible, keeping
> dynamic variables for ones that the parser cannot pick up (eg: created by
> "eval"). Dynamic variables are accessed significantly slower than local
> ones, because a linear search is done (in 1.8 anyhow). This change would
> eliminate the unnecessary (and ugly) initialization of a variable before a
> loop simply to make it "local" and hence faster. Furthermore it would
> probably eliminate the use of dynamic variables completely in most loops,
> which would mean that a new block of dynamic variables could be created
> lazily for extra efficiency. Does YARV address this at all?

We've done this in JRuby already; all logic for "dynamic vars" is the 
same as for "local vars", rather than the linear search done before. I 
believe YARV also addresses this for dvars, since in the YARV bytecode 
dvars are specified by two numbers: var index and depth. We have the 
same logic in JRuby today.

-- 
Charles Oliver Nutter, JRuby Core Developer
Blogging on Ruby and Java @ headius.blogspot.com
Help spec out Ruby today! @ www.headius.com/rubyspec
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