Re: map-par slower than map

[Damien Mattei <damien.mattei@gmail.com>]

Hello,

sorry for my late answer ( i wrote the code friday but i could only debug
today, being busy and on travel last week-end)

i modified my code to works with 'futures' , the speed is now incredible
!!! (and it computes exact)
the speed seems multiplied by even more than the number of CPUs (6):
cat /proc/cpuinfo  | grep processor
processor : 0
processor : 1
processor : 2
processor : 3
processor : 4
processor : 5

https://github.com/damien-mattei/library-FunctProg/blob/master/guile/logiki%2B.scm#L1900

(declare minterms-vector unified-minterms-vector-1)

(define (funct-unify-minterms-set-1-unit-future set1 set2)

  {function-unify-minterms-list <+ (λ (L) (apply
function-unify-two-minterms-and-tag L))}

  ;; note : sorting is useless

  {minterms-set <+ (product-set-with-set-imperative-sorted set1 set2)}
;;(product-set-with-set-imperative set1 set2)} ;;(product-set-with-set set1
set2)} ;;(associate-set-with-set set1 set2)} ;; set multiplication : create
list of pair of minterms

  {minterms-vector <- (list->vector minterms-set)}

  {minterms-vector-length <+ (vector-length minterms-vector)}

  {nb-procs <+ (current-processor-count)}

  {segmts <+ (segment 0 {minterms-vector-length - 1} nb-procs)} ;; compute
the segments

  {unified-minterms-vector-1 <- (make-vector minterms-vector-length #f)}

  (run-in-parallel segmts proc-unify-minterms-seg) ;; run the parallel code

  {unified-minterms-set-1 <+ (vector->list unified-minterms-vector-1)}

  {unified-minterms-set-2 <+ (filter (λ (x) x) unified-minterms-set-1)} ;;
remove #f results

  {unified-minterms-set <+ (remove-duplicates-sorted
unified-minterms-set-2)} ;; uniq

  unified-minterms-set)

i keeped your 'segment' definitions to index an array of data after convert
it from list to vector (list->vector) which probably consume additional
time on big data list ( i had more than 1000000 element list lengths at
some point)

i used a simplified version of run-in parallel (that do not do 'reduce
after processing data):

https://github.com/damien-mattei/library-FunctProg/blob/master/guile/logiki%2B.scm#L1794

the computation on a segment is done by those functions:

https://github.com/damien-mattei/library-FunctProg/blob/master/guile/logiki%2B.scm#L1842

{function-unify-minterms-list <+ (λ (L) (apply
function-unify-two-minterms-and-tag L))}

;; proc to be called with futures
(define (proc-unify-minterms-seg seg)
  {start <+ (segment-start seg)}
  {end <+ (segment-end seg)}
  (for ({i <+ start} {i <= end} {i <- {i + 1}})
       {mtL <+ {minterms-vector[i]}}
       {unified-minterms-vector-1[i] <- (function-unify-minterms-list
mtL)}))


i use those code in another program symbolically to compute a value named
Cn:

C0 = T
C1 = T
C2 = T
C3 = (B1 ∨ B2)
C4 = (B2 ∨ (B1 ∧ B3))
C5 = ((B1 ∧ B3) ∨ (B2 ∧ B3) ∨ (B2 ∧ B4) ∨ (B3 ∧ B4))
C6 = ((B1 ∧ B3 ∧ B5) ∨ (B2 ∧ B3 ∧ B5) ∨ (B2 ∧ B4) ∨ (B3 ∧ B4) ∨ (B4 ∧ B5))
C7 = ((B1 ∧ B3 ∧ B5) ∨ (B2 ∧ B3 ∧ B5) ∨ (B2 ∧ B4 ∧ B6) ∨ (B3 ∧ B4 ∧ B6) ∨
(B4 ∧ B5) ∨ (B5 ∧ B6))
C8 = ((B1 ∧ B3 ∧ B5 ∧ B7) ∨ (B2 ∧ B3 ∧ B5 ∧ B7) ∨ (B2 ∧ B4 ∧ B6) ∨ (B3 ∧ B4
∧ B6) ∨ (B4 ∧ B5 ∧ B7) ∨ (B5 ∧ B6) ∨ (B6 ∧ B7))
C9 = ((B1 ∧ B3 ∧ B5 ∧ B7) ∨ (B2 ∧ B3 ∧ B5 ∧ B7) ∨ (B2 ∧ B4 ∧ B6 ∧ B8) ∨ (B3
∧ B4 ∧ B6 ∧ B8) ∨ (B4 ∧ B5 ∧ B7) ∨ (B5 ∧ B6 ∧ B8) ∨ (B6 ∧ B7) ∨ (B7 ∧ B8))

from C1 to C9 used to be fast,less than  a minute for the whole with or
without //

C10 = ((B1 ∧ B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B2 ∧ B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B2 ∧ B4 ∧ B6
∧ B8) ∨ (B3 ∧ B4 ∧ B6 ∧ B8) ∨ (B4 ∧ B5 ∧ B7 ∧ B9) ∨ (B5 ∧ B6 ∧ B8) ∨ (B6 ∧
B7 ∧ B9) ∨ (B7 ∧ B8) ∨ (B8 ∧ B9))

C10 takes a few minutes

but C11 used to take one day before // with 'future' and i got now the
result during less than one hour!!!

C11 = ((B1 ∧ B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B10 ∧ B2 ∧ B4 ∧ B6 ∧ B8) ∨ (B10 ∧ B3 ∧
B4 ∧ B6 ∧ B8) ∨ (B10 ∧ B5 ∧ B6 ∧ B8) ∨ (B10 ∧ B7 ∧ B8) ∨ (B10 ∧ B9) ∨ (B2 ∧
B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B4 ∧ B5 ∧ B7 ∧ B9) ∨ (B6 ∧ B7 ∧ B9) ∨ (B8 ∧ B9))

i never got C12 in the past ,even with 7 days of computation! and i got it
today during the lunchbreak !!!

C12 = ((B1 ∧ B11 ∧ B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B10 ∧ B11) ∨ (B10 ∧ B2 ∧ B4 ∧ B6 ∧
B8) ∨ (B10 ∧ B3 ∧ B4 ∧ B6 ∧ B8) ∨ (B10 ∧ B5 ∧ B6 ∧ B8) ∨ (B10 ∧ B7 ∧ B8) ∨
(B10 ∧ B9) ∨ (B11 ∧ B2 ∧ B3 ∧ B5 ∧ B7 ∧ B9) ∨ (B11 ∧ B4 ∧ B5 ∧ B7 ∧ B9) ∨
(B11 ∧ B6 ∧ B7 ∧ B9) ∨ (B11 ∧ B8 ∧ B9))

(note that a wise people can find a general formula for Cn based on Cn-1
but that is another (mathematical) story....)

i'm computing C13 but i see that it consumes 12gb out of 16gb of my system
! and stopped on the linux box :
GC Warning: Repeated allocation of very large block (appr. size 510935040):
May lead to memory leak and poor performance
Processus arrêté
but still running on the Mac laptop...ok will see that but i think that the
data set is now huge and there is noting that can be done with that...

note that there is still an hash table used in
function-unify-two-minterms-and-tag and i will use another data structure
and algo to avoid that, i feared that the concurrent access to hash table
can cause the guile 'future' to crash or fails or to slow down the process
but not! result is incredibly fast.Also i use continuation and i read it
can cause problem with 'future' i will improve that too...

I will see where i can improve the algo and data structure to optimize
again but this is already really good.

Thanks

Damien


On Fri, Oct 14, 2022 at 10:39 AM Zelphir Kaltstahl <
zelphirkaltstahl@posteo.de> wrote:

> Hello Damien,
> On 10/14/22 10:21, Damien Mattei wrote:
>
> yes Zelphir i think there is a problem in the threading part of guile,
> whatever the code is ,it run well the first time, and after is unstable.
> Long ago at the very begin of Java language on my master project at
> university i experienced same problem with Java "green" threads, under
> windows and/or linux ,i can't remember.
>
> I'm trying your code and future, which have perheaps also the portability
> with other schemes, future can provide "light" // , with carefull code it
> could be ok.
>
> in your segment.scm code ,is segment-count possibly replaced by the number
> of available CPUs or nodes, if i understand well?
>
> Regards,
> Damien
>
> Correct. For each segment one future is used.
>
> However, there are scenarios, where one would rather want to interleave
> the numbers of the whole range, to have a "fairer" workload per future, for
> example:
>
> (1 2 3 4 5 6 7 8 9)
>
> -> (1 4 7), (2 5 8), (3 6 9)
>
> instead of
>
> -> (1 2 3) (4 5 6) (7 8 9)
>
> (I seem to remember this to be the case for Mandelbrot set calculations,
> but might be wrong.)
>
> But that is all a matter of forming some segments and what a segment is,
> not really part of the logic of creating futures. So one could create then
> in any way that fits ones use-case. I have not generalized that segment
> logic that far, but it is doable.
>
> Anyway, if anyone more knowledgeable could chime in on what the
> performance differences between futures and parallel map are, that would be
> great! Or pointing out some flaws that this kind of future usage might
> have. Or when the point is reached to switch to guile-fibers library.
>
> Regards,
> Zelphir
>
> --
> repositories: https://notabug.org/ZelphirKaltstahl
>
>