[plt-scheme] Futures performance

Robby, once we make the edit, both Jon and I see results very similar
to the original report.

Shriram

On Thu, May 27, 2010 at 11:53 PM, Robby Findler
<robby at eecs.northwestern.edu> wrote:
> Since we are having trouble reproducing the behavior you are seeing,
> perhaps you can supply us with more information? What version are you
> running? Are you running inside drscheme or not?
>
> Also note that if you pass the flags
>
>  -W debug
>
> to mzscheme you can see if your future threads are blocking.
>
> Robby
>
> 2010/5/27 Groshev Dmitry <a2alt at yandex.ru>:
>>> On Wed, May 26, 2010 at 11:44 PM, Jon Rafkind  wrote:
>>>  > On 05/25/2010 08:53 PM, Groshev Dmitry wrote:
>>>  >>
>>>  >> What am I doing wrong? Here is the code and some tests:
>>>  >>
>>>  >> (require scheme/future)
>>>  >>
>>>  >> (define (fib n)
>>>  >>   (case n
>>>  >>     [(0) 0]
>>>  >>     [(1) 1]
>>>  >>     [else (let ((a (fib (- n 1)))
>>>  >>                 (b (fib (- n 2))))
>>>  >>             (+ a b))]))
>>>  >>
>>>  >> (define (fibp n)
>>>  >>   (case n
>>>  >>     [(0) 0]
>>>  >>     [(1) 1]
>>>  >>     [else (let ((a (future (lambda () (fib (- n 1)))))
>>>  >>                 (b (future (lambda () (fib (- n 2))))))
>>>  >>             (+ (touch a) (touch b)))]))
>>>  >>
>>>  >>
>>>  >>>
>>>  >>> (time (fib 30))
>>>  >>>
>>>  >>
>>>  >> cpu time: 546 real time: 539 gc time: 0
>>>  >> 832040
>>>  >>
>>>  >>>
>>>  >>> (time (fibp 30))
>>>  >>>
>>>  >>
>>>  >> cpu time: 8986 real time: 7814 gc time: 391
>>>  >> 832040
>>>  >>
>>>  >
>>>  > Is that actually the code you are running? If I take your code verbatim I
>>>  > get times like these
>>>  >
>>>  > ;; I set n to 40 so you can see a real difference
>>>  > cpu time: 6100 real time: 6448 gc time: 0
>>>  > 102334155
>>>  > cpu time: 6132 real time: 3995 gc time: 0
>>>  > 102334155
>>>  >
>>>  >
>>>  > But if I change the code so that `fibp' makes recursive calls to `fibp'
>>>  > instead of `fib' then I see `fibp' taking much longer.
>>>  > ;; n = 33
>>>  > cpu time: 496 real time: 498 gc time: 0
>>>  > 3524578
>>>  > cpu time: 17429 real time: 18720 gc time: 748
>>>  > 3524578
>>>  >
>>>
>>>  Last I heard, you can't create futures within a future (the runtime
>>>  blocks the future that tried).
>>>
>>>  If that's still the case, it explains why you see no speedup. I don't
>>>  know if that's enough to cause the slowdown you're seeing.
>>>
>>>  > Which is similar to your results. What sort of machine are you on? I'm on a
>>>  > dual-core amd 1.8ghz laptop.
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>> Yes, it must be "fibp", not "fib".
>> Runtime blocking is an explanation, but it seems to me that there is still to much slowdown for just blocking.
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