Looks like all but about 2x of the overhead is in the dict-update!
contract, which is this:
(->i ([d (dict-implements/c 'dict-set!)]
[k (d) (dict-key-contract d)]
[update (d) (-> (dict-value-contract d) (dict-value-contract d))])
([default (d) (or/c (dict-value-contract d) (->
(dict-value-contract d)))]) ;; use if/c
[_r void?])
Looks like some improvements (probably 7056cd5f2) since 6.3 have
shaved 10% of the time off. Not enough, I know.
->i doesn't participate in a relevant contract-system optimization
that -> and ->* do, but it could. That would improve things by about
2x I guess.
Robby
Robby
On Wed, Jan 6, 2016 at 9:23 AM, Matthias Felleisen <[email protected]> wrote:
>
> I ran across the snippet of code below (I turned it into a performance
> benchmark) and was amazed at how much slower the code ran after making it
> readable with dict!: I am seeing a factor of 20x and 40x depending on what
> exactly is run. Can anything be done about this?
>
>
> #lang racket
>
> (define (create n)
> (define i 0)
> (define sample (make-vector n))
> (lambda (item)
> (set! i (+ i 1))
> (vector-set! sample (if (<= i n) (sub1 i) (quotient n 2)) item)
> sample))
>
> (define counts (make-vector 10 0))
>
> (define-syntax-rule
> (measure n d update)
> (begin
> (collect-garbage)
> (collect-garbage)
> (collect-garbage)
> (time
> (for ([i n])
> (define f (create 3))
> (define sample (for/last ([digit 10]) (f digit)))
> (for ([d sample])
> update)))))
>
> ;; I don't want more HO overhead
> (define n 1000000)
> (measure n d (vector-set! counts d (add1 (vector-ref counts d))))
> (measure n d (dict-update! counts d add1))
>
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