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Re: map-par slower than map
From: |
Damien Mattei |
Subject: |
Re: map-par slower than map |
Date: |
Thu, 13 Oct 2022 12:44:42 +0200 |
i trying to use your code but it seems there is a ) mismatch somewhere?
On Wed, Oct 12, 2022 at 11:55 PM Olivier Dion <olivier.dion@polymtl.ca>
wrote:
> On Wed, 12 Oct 2022, Damien Mattei <damien.mattei@gmail.com> wrote:
> > Hello,
> > all is in the title, i test on a approximately 30000 element list , i got
> > 9s with map and 3min 30s with par-map on exactly the same piece of
> > code!?
>
> I can only speculate here. But trying with a very simple example here:
> --8<---------------cut here---------------start------------->8---
> (use-modules (statprof))
> (statprof (lambda () (par-map 1+ (iota 300000))))
> --8<---------------cut here---------------end--------------->8---
>
> Performance are terrible. I don't know how par-map is implemented, but
> if it does 1 element static scheduling -- which it probably does because
> you pass a linked list and not a vector -- then yeah you can assure that
> thing will be very slow.
>
> You're probably better off with dynamic scheduling with vectors. Here's
> a quick snippet I made for static scheduling but with vectors. Feel
> free to roll your own.
>
> --8<---------------cut here---------------start------------->8---
> (use-modules
> (srfi srfi-1)
> (ice-9 threads))
>
> (define* (par-map-vector proc input
> #:optional
> (max-thread (current-processor-count)))
>
> (let* ((block-size (quotient (vector-length input) max-thread))
> (rest (remainder (vector-length input) max-thread))
> (output (make-vector (vector-length input) #f)))
> (when (not (zero? block-size))
> (let ((mtx (make-mutex))
> (cnd (make-condition-variable))
> (n 0))
> (fold
> (lambda (scale output)
> (begin-thread
> (let lp ((i 0))
> (when (< i block-size)
> (let ((i (+ i (* scale block-size))))
> (vector-set! output i (proc (vector-ref input i))))
> (lp (1+ i))))
> (with-mutex mtx
> (set! n (1+ n))
> (signal-condition-variable cnd)))
> output)
> output
> (iota max-thread))
> (with-mutex mtx
> (while (not (< n max-thread))
> (wait-condition-variable cnd mtx))))
> (let ((base (- (vector-length input) rest)))
> (let lp ((i 0))
> (when (< i rest)
> (let ((i (+ i base)))
> (vector-set! output i (proc (vector-ref input i))))
> (lp (1+ i)))))
> output))
> --8<---------------cut here---------------end--------------->8---
>
> --
> Olivier Dion
> oldiob.dev
>
- Re: map-par slower than map, (continued)
- Re: map-par slower than map, Zelphir Kaltstahl, 2022/10/24
- Re: map-par slower than map, Damien Mattei, 2022/10/24
- Re: map-par slower than map, Mikael Djurfeldt, 2022/10/25
- Re: map-par slower than map, Mikael Djurfeldt, 2022/10/25
- Re: map-par slower than map, Damien Mattei, 2022/10/25
- Re: map-par slower than map, Maxime Devos, 2022/10/12
Re: map-par slower than map, Olivier Dion, 2022/10/12
- Re: map-par slower than map, Damien Mattei, 2022/10/13
- Re: map-par slower than map,
Damien Mattei <=
- Re: map-par slower than map, Olivier Dion, 2022/10/13
- Message not available
- Fwd: map-par slower than map, Damien Mattei, 2022/10/13
- Re: map-par slower than map, Damien Mattei, 2022/10/13
- Re: map-par slower than map, Olivier Dion, 2022/10/13
- Re: map-par slower than map, Damien Mattei, 2022/10/13
- Re: map-par slower than map, Olivier Dion, 2022/10/13
- Re: map-par slower than map, Damien Mattei, 2022/10/13
- Re: map-par slower than map, Damien Mattei, 2022/10/13