I don't think the parameter overhead is relevant. In Jay's post, he performs 100k parameter accesses, and it takes 16 milliseconds; we can reasonably extrapolate 160 msec for 1M accesses. Patrick's generator example yields 1M times, and takes 18 seconds --- 100x the parameter overhead.
I agree with others that the cost of capturing continuations is the culprit in this case. The run-time system has support for faster continuations that work in constrained settings (currently used to implement futures), and it might be possible to make those continuations kick in work for a typical generator, but I'm not sure. Meanwhile, it might be interesting to try implementing a `generator' form that rewrites its body to implement `yield's that are syntactically apparent (after local-expansion), leaving parameter and continuations to handle the general case. At Tue, 18 Sep 2012 07:07:51 -0400, Greg Hendershott wrote: > This stuff is still over my head; I'm at that "know just enough to be > dangerous" stage. With that caveat: > > Jay's blog post > http://jeapostrophe.github.com/blog/2012/07/25/cont-marks2/ mentions > that parameters can be >10X slower than dynamic-wind. > > In generator.rkt I notice an early version that didn't support > multiple values. The new version does, keeping a "yielder" proc in a > parameter. > > Could a single-valued generator yield be faster enough? Or am I > misapplying my misunderstanding? :) > > On Sun, Sep 16, 2012 at 11:15 AM, Eli Barzilay <e...@barzilay.org> wrote: > > Two hours ago, Patrick Useldinger wrote: > >> Hello > >> > >> I have a Python program doing some intensive computing and would > >> like to port it to Racket for performance reasons. > >> > >> I use a generator in Python which has a very low overhead. While > >> writing some test programs, I seem to have an substantial overhead > >> on using generators in Racket: > >> [...] > > > > IIRC, Python optimizes generators in some ways when possible so when > > they're used with loops there's no big overhead. The racket > > generators are implemented with continuations and the cost that comes > > with that is unfortunately pretty high. If you need performance, your > > best bet is probably to translate things to `for...' loops if > > possible. > > > > -- > > ((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay: > > http://barzilay.org/ Maze is Life! > > ____________________ > > Racket Users list: > > http://lists.racket-lang.org/users > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
