From: Damien Mattei <damien.mattei@gmail.com>
Cc: guile-user <guile-user@gnu.org>, guile-devel <guile-devel@gnu.org>
Subject: Re: map-par slower than map
Date: Thu, 13 Oct 2022 09:40:28 +0200 [thread overview]
Message-ID: <CADEOadcxSDvWEd7fQMWUAPQXejNU8WV_AU9OV7fh+qu_Xt_1yQ@mail.gmail.com> (raw)
In-Reply-To: <87bkqg7lmp.fsf@laura>
ok , i think the problem comes both from my code and from guile parmap so.
Obviously parmap could be slower on other codes because of the nature of
list i think, it is hard to split a list in sublist and send them to thread
and after redo a single list, i better use vector.
As mentioned and forget by me, i apologize, i use an hash table which is a
global variable and mutex can be set on it , no dead lock , here but it
slow down the code than it is dead for speed , but not locked.
The examples given are good but i do not want to write long and specific
code for //, for // must a ssimple as OpenMP directives (on arrays) not be
a pain in the ass like things i already did at work with GPUs in C or
Fortran,that's nightmare and i do not want to have this in functional
programming.
ok i will try to modify the code but i do not think there is easy solution
to replace the hash table, any structure i would use would be global and
the problem (this function is not pure, it does a side-effect),at the end i
do not think this code could be // but i'm not a specialist of //. I think
this is a parallelization problem, how can we deal with a global variable
such as an hash table?
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
>
next prev parent reply other threads:[~2022-10-13 7:40 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-12 17:19 map-par slower than map Damien Mattei
2022-10-12 18:45 ` Maxime Devos
2022-10-12 20:20 ` Damien Mattei
2022-10-12 20:27 ` Damien Mattei
2022-10-12 21:29 ` Zelphir Kaltstahl
2022-10-14 8:21 ` Damien Mattei
2022-10-14 8:38 ` Zelphir Kaltstahl
2022-10-17 13:17 ` Damien Mattei
2022-10-22 16:01 ` Damien Mattei
2022-10-23 1:06 ` Damien Mattei
2022-10-23 23:18 ` Zelphir Kaltstahl
2022-10-24 3:56 ` Keith Wright
2022-10-24 7:03 ` Zelphir Kaltstahl
2022-10-24 4:39 ` Damien Mattei
2022-10-25 9:07 ` Mikael Djurfeldt
2022-10-25 9:11 ` Mikael Djurfeldt
2022-10-25 14:09 ` Damien Mattei
2022-11-10 10:32 ` Damien Mattei
2022-11-10 10:41 ` Damien Mattei
2022-11-10 10:52 ` Zelphir Kaltstahl
2022-11-10 13:36 ` Damien Mattei
2022-11-10 17:07 ` Olivier Dion via General Guile related discussions
2022-11-11 10:26 ` Damien Mattei
2022-11-11 12:25 ` Zelphir Kaltstahl
2022-11-11 13:36 ` Damien Mattei
2022-11-11 13:37 ` Damien Mattei
2022-11-13 8:23 ` Damien Mattei
2022-10-12 21:44 ` Maxime Devos
2022-10-12 21:55 ` Olivier Dion via Developers list for Guile, the GNU extensibility library
2022-10-13 7:40 ` Damien Mattei [this message]
2022-10-13 8:20 ` Damien Mattei
2022-10-13 9:10 ` Olivier Dion via Developers list for Guile, the GNU extensibility library
2022-10-13 10:44 ` Damien Mattei
2022-10-13 11:00 ` Olivier Dion via Developers list for Guile, the GNU extensibility library
[not found] ` <CADEOadfovi8s3OxRcssWOuOW8jjHoL9Z7pD_5FstSm=ZkBHP8g@mail.gmail.com>
2022-10-13 11:57 ` Fwd: " Damien Mattei
2022-10-13 12:36 ` Damien Mattei
2022-10-13 12:41 ` Olivier Dion via Developers list for Guile, the GNU extensibility library
2022-10-13 13:43 ` Damien Mattei
2022-10-13 14:06 ` Olivier Dion via Developers list for Guile, the GNU extensibility library
2022-10-13 14:10 ` Damien Mattei
2022-10-13 14:21 ` Damien Mattei
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