[racket] performance of iteration through a vector
Usually you'll get the best performance from `for` loops by using the in-* iterators.
In this case, you can use `in-vector` [1], which on my machine is faster:
(let ((t (current-inexact-milliseconds))
(sum 0))
(for ((j (in-range 1000000)))
(for ((v (in-vector vec)))
(set! sum (+ sum v))))
(displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
I assume this is a synthetic example, but you can also improve performance by using appropriate versions of `for`. This is faster than the last one:
(let ((t (current-inexact-milliseconds)))
(for*/fold ([sum 0])([j (in-range 1000000)][v (in-vector vec)])
(+ sum v))
(displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
And this is faster still:
(let ((t (current-inexact-milliseconds)))
(for*/sum ([j (in-range 1000000)][v (in-vector vec)])
v)
(displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
[1] http://docs.racket-lang.org/reference/sequences.html?q=in-vector#%28def._%28%28lib._racket%2Fprivate%2Fbase..rkt%29._in-vector%29%29
On Aug 30, 2014, at 3:54 PM, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:
> Hello,
>
> Consider the following program:
>
> (define n 100)
> (define vec (for/vector ((i (in-range n))) i))
>
> (let ((t (current-inexact-milliseconds))
> (sum 0))
> (for ((j (in-range 1000000)))
> (for ((i (in-range n)))
> (set! sum (+ sum (vector-ref vec i)))))
> (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
>
> (let ((t (current-inexact-milliseconds))
> (sum 0))
> (for ((j (in-range 1000000)))
> (for ((v vec))
> (set! sum (+ sum v))))
> (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
>
>
> On my system (64-bit linux, Racket 6.1.0.2), it gives the following result:
>
> 1.016682861328125
> 6.3261611328125
>
>
> So we can make a conclusion that (for ((v vec)) ...) is
> 6x slower than (for ((i (in-range n))) ... (vector-ref vec i) ...)
> Is it normal? Would you advise to use the explicit (vector-ref)
> when performance matters?
>
> Best regards
>
> Dmitry
>
> ____________________
> Racket Users list:
> http://lists.racket-lang.org/users
On Aug 30, 2014, at 3:54 PM, Dmitry Pavlov <dpavlov at ipa.nw.ru> wrote:
> Hello,
>
> Consider the following program:
>
> (define n 100)
> (define vec (for/vector ((i (in-range n))) i))
>
> (let ((t (current-inexact-milliseconds))
> (sum 0))
> (for ((j (in-range 1000000)))
> (for ((i (in-range n)))
> (set! sum (+ sum (vector-ref vec i)))))
> (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
>
> (let ((t (current-inexact-milliseconds))
> (sum 0))
> (for ((j (in-range 1000000)))
> (for ((v vec))
> (set! sum (+ sum v))))
> (displayln (/ (- (current-inexact-milliseconds) t) 1000.0)))
>
>
> On my system (64-bit linux, Racket 6.1.0.2), it gives the following result:
>
> 1.016682861328125
> 6.3261611328125
>
>
> So we can make a conclusion that (for ((v vec)) ...) is
> 6x slower than (for ((i (in-range n))) ... (vector-ref vec i) ...)
> Is it normal? Would you advise to use the explicit (vector-ref)
> when performance matters?
>
> Best regards
>
> Dmitry
>
> ____________________
> Racket Users list:
> http://lists.racket-lang.org/users
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