Re: Ruby performance improvements

----- 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.

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?

> I hope that perf changes like these can get into the 1.8 line. There's a
> lot of low-hanging fruit in Ruby 1.8's current design that could improve
> performance until 2.0 is around.
Agreed, though how much effort should be put in really depends on how long
it will be till 2.0 is stable.

Mike