[racket] Performance. Higher-order function

Because build-string calls an unknown function 1000 x 100000 times, and an unknown function call is expensive. 

Racket could possible collapse all modules and perform additional in-lining optimizations eventually, which may help here. But it doesn't yet. 

-- Matthias



On Aug 3, 2014, at 5:15 AM, Roman Klochkov wrote:

> Are higher order function always slow?
> 
> Made small test:
> test1 -- unfamous set-in-the-loop accumulating
> test2 -- built-in build-string
> test3 -- manually written build-string with the same code as in test1
> ----
> (define (test1 n)
> (define res (make-string n))
>     (for ([i (in-range n)])
>         (string-set! res i (integer->char i)))
> res)
> 
> (define (test2 n)
>     (build-string n integer->char))
> 
> (define (build-string1 n proc)
>     (define res (make-string n))
>     (for ([i (in-range n)])
>         (string-set! res i (proc i)))
>     res)
> 
> (define (test3 n)
>     (build-string1 n integer->char))
> 
> (time (for ([i 100000]) (test1 100)))
> (time (for ([i 100000]) (test1 100)))
> (time (for ([i 100000]) (test1 100)))
> (displayln "")
> (time (for ([i 100000]) (test2 100)))
> (time (for ([i 100000]) (test2 100)))
> (time (for ([i 100000]) (test2 100)))
> (displayln "")
> (time (for ([i 100000]) (test3 100)))
> (time (for ([i 100000]) (test3 100)))
> (time (for ([i 100000]) (test3 100)))
> ----
> Tested on Linux x32
> 
> $ /usr/racket/bin/racket 
> Welcome to Racket v6.1.
> > (enter! "test") 
> cpu time: 360 real time: 469 gc time: 64
> cpu time: 212 real time: 209 gc time: 0
> cpu time: 208 real time: 208 gc time: 0
> 
> cpu time: 400 real time: 402 gc time: 0
> cpu time: 380 real time: 382 gc time: 4
> cpu time: 384 real time: 383 gc time: 0
> 
> cpu time: 524 real time: 529 gc time: 4
> cpu time: 468 real time: 470 gc time: 8
> cpu time: 412 real time: 414 gc time: 12
> 
> ---
> 
> So I see, that build-string version is about two times slower, than set-in-the-loop. Why so much? I expected about 10-20% difference.
> 
> -- 
> Roman Klochkov
> ____________________
>  Racket Users list:
>  http://lists.racket-lang.org/users

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