Re: map-par slower than map

[Damien Mattei]

Hello Mikael,

your message comes very well because i decided yesterday,partly due to the
discussion in mailing list, to review all the // method used in my code and
to use them to perform benchmark to see which one is preferable to use with
the algorithmic problem of putting a logic expression in its canonical
minimal disjunctive or conjunctive form.

I used 4 methods:
-sequential (map with no //)
-par-map (//)
-threads  (//)
-futures (//)

But, of course, the data structure is not the same now, it will be lists
with sequential and par-map and vectors with threads and futures, as i
already experimented problems (blocking, crashing,false results) with some
(threads,futures) . Also i have solved the concurrent access problem to the
hash table with lists or vectors depending if i use map or par-map or
futures and threads, but the algorithm remains the same in all case.

I computed from C1,C2,C3 ... to C12 (i do not write the logical expressions
here, some peoples seeing those infix mathematical expression coming in the
mailing list as drones in the peaceful sky of the lambda calculus
expressions ;-) ) but here is the results:

map: 10' 17" for C12 (5" for C10)
par-map: 1'21" for C10, more than 2h 40' for  C12
threads: blocks randomly before C7 (works but is not reentrant, perheaps a
problem in the code i use with thread programming)
futures:8" for C12, 25" for C13,2' for C14,7' for C15...

the best performance are,from far, with futures and the code provided by
Zelphir.

on a 6 cores processor with 16Gb of memory.note at C15 computation the
memory containing minterms and logical expression not simplified is about 3
Gb:
  PID UTIL.     PR  NI    VIRT    RES    SHR S  %CPU  %MEM    TEMPS+ COM.


  61051 mattei    20   0 *3339388*   2,7g  22368 R 463,1  *17,2 * 33:27.92
*guile*

cf :
https://en.wikipedia.org/wiki/Quine%E2%80%93McCluskey_algorithm#Complexity

what i will do is write a Python version of the computation of Cn that uses
the Sympy minimal disjunctive normal form procedure of the Sympy library ,
first to check my scheme code result and perheaps compare the speed, i know
python is slow but as it is a library (compiled? but written in python as
far as i know?), well, i'm a bit nervous to compare the speed between
Python and Scheme...

Best regards,
Damien

On Tue, Oct 25, 2022 at 11:11 AM Mikael Djurfeldt <mikael@djurfeldt.com>
wrote:

> Also, I would believe that any crashes in this context are neither due to
> the futures implementation nor par-map et al. I would think that crashes
> are due to the Guile basic thread support itself.
>
> On Tue, Oct 25, 2022 at 11:07 AM Mikael Djurfeldt <mikael@djurfeldt.com>
> wrote:
>
>> A piece of background on par-map:
>>
>> When I introduced par-map et al the only ambition was to have simple
>> language constructs to invoke parallelism. The use case I had in mind was
>> course grained parallelism where each piece of work is somewhat
>> substantial. Back then, a thread was launched for each piece of work,
>> however there was also a thread pool such that not all of the overhead of
>> launching new threads always was required.
>>
>> Since then, par-map has been rewritten (by others) to be based on
>> futures. (And now the thread pool is localized in the futures
>> implementation---as "workers".) Looking in the code now, I think it is fair
>> to say that it is still intended for coarse grained parallelism. There is
>> some heavy lifting going on with mutexes and condition variables as well as
>> shuffling around with list pairs.
>>
>> So, applying par-map on a huge list with small amount of work per item
>> was never and still isn't the intended use case.
>>
>> It would of course be interesting if the code could be improved to
>> support fine grained parallelism. :-)
>>
>> Best regards,
>> Mikael
>>
>> On Wed, Oct 12, 2022 at 11:30 PM Zelphir Kaltstahl <
>> zelphirkaltstahl@posteo.de> wrote:
>>
>>> Hi!
>>>
>>> On 10/12/22 22:27, Damien Mattei wrote:
>>> >
>>> https://github.com/damien-mattei/library-FunctProg/blob/master/guile/logiki%2B.scm#L1674
>>> >
>>> > i commited the current version of code here with all files but it is
>>> > huge.... :-/
>>> >
>>> > On Wed, Oct 12, 2022 at 10:20 PM Damien Mattei <
>>> damien.mattei@gmail.com>
>>> > wrote:
>>> >
>>> >> Mutex? i do not think code has situation where dead lock could
>>> happen, it
>>> >> is a code about minimalising logic expressions, it uses minterms ,
>>> minterms
>>> >> set is a set of minterms :like this:
>>> >>
>>> >> example:
>>> >> ((1 1 0) (1 1 1)) will be unified : (1 1 x)
>>> >> because 0 and 1 are replaced by x
>>> >> the minterms-set could have thousands of pair (mathematic not lisp)
>>> >> minterms to unify
>>> >> if there is more than one x as result there is no need to continue so
>>> i
>>> >> escape with a continuation:
>>> >>
>>> >> minterms-set =
>>> >> {
>>> >> ((1 0 1 0) (1 1 1 0))
>>> >> ((1 0 1 0) (1 1 0 1))
>>> >> ((1 0 1 0) (1 0 1 1))
>>> >> ((1 0 1 0) (0 1 1 1))
>>> >> ((0 1 1 0) (1 1 1 0))
>>> >> ((0 1 1 0) (1 1 0 1))
>>> >> ((0 1 1 0) (1 0 1 1))
>>> >> ((0 1 1 0) (0 1 1 1))
>>> >> ((0 1 0 1) (1 1 1 0))
>>> >> ((0 1 0 1) (1 1 0 1))
>>> >> ((0 1 0 1) (1 0 1 1))
>>> >> ((0 1 0 1) (0 1 1 1))
>>> >> ((0 0 1 1) (1 1 1 0))
>>> >> ((0 0 1 1) (1 1 0 1))
>>> >> ((0 0 1 1) (1 0 1 1))
>>> >> ((0 0 1 1) (0 1 1 1))
>>> >> }
>>> >>
>>> >> replace { } by () to have the list, other example at another level :
>>> >>
>>> >> minterms-set =
>>> >> {
>>> >> ((0 x 1 1) (x 1 1 1))
>>> >> ((0 x 1 1) (1 x 1 1))
>>> >> ((0 x 1 1) (1 1 x 1))
>>> >> ((0 x 1 1) (1 1 1 x))
>>> >> ((x 0 1 1) (x 1 1 1))
>>> >> ((x 0 1 1) (1 x 1 1))
>>> >> ((x 0 1 1) (1 1 x 1))
>>> >> ((x 0 1 1) (1 1 1 x))
>>> >> ((0 1 x 1) (x 1 1 1))
>>> >> ((0 1 x 1) (1 x 1 1))
>>> >> ((0 1 x 1) (1 1 x 1))
>>> >> ((0 1 x 1) (1 1 1 x))
>>> >> ((x 1 0 1) (x 1 1 1))
>>> >> ((x 1 0 1) (1 x 1 1))
>>> >> ((x 1 0 1) (1 1 x 1))
>>> >> ((x 1 0 1) (1 1 1 x))
>>> >> ((0 1 1 x) (x 1 1 1))
>>> >> ((0 1 1 x) (1 x 1 1))
>>> >> ((0 1 1 x) (1 1 x 1))
>>> >> ((0 1 1 x) (1 1 1 x))
>>> >> ((x 1 1 0) (x 1 1 1))
>>> >> ((x 1 1 0) (1 x 1 1))
>>> >> ((x 1 1 0) (1 1 x 1))
>>> >> ((x 1 1 0) (1 1 1 x))
>>> >> ((1 0 1 x) (x 1 1 1))
>>> >> ((1 0 1 x) (1 x 1 1))
>>> >> ((1 0 1 x) (1 1 x 1))
>>> >> ((1 0 1 x) (1 1 1 x))
>>> >> ((1 x 1 0) (x 1 1 1))
>>> >> ((1 x 1 0) (1 x 1 1))
>>> >> ((1 x 1 0) (1 1 x 1))
>>> >> ((1 x 1 0) (1 1 1 x))
>>> >> }
>>> >>
>>> >> here we see some minterms are already unified
>>> >>
>>> >>   it is not easy to read even by me because i wrote the code many
>>> years ago
>>> >> and is split in many files, but here it is:
>>> >>
>>> >> (par-map function-unify-minterms-list minterms-set)
>>> >>
>>> >> {function-unify-minterms-list <+ (λ (L) (apply
>>> >> function-unify-two-minterms-and-tag L))}
>>> >>
>>> >> (define (unify-two-minterms mt1 mt2)
>>> >>    (function-map-with-escaping-by-kontinuation2
>>> >>   (macro-function-compare-2-bits-with-continuation) mt1 mt2))
>>> >>
>>> >> ;; (function-map-with-escaping-by-kontinuation2
>>> >> (macro-function-compare-2-bits-with-continuation)   '(1 1 0 1 0 1 1
>>> 0) '(1
>>> >> 1 0 1 1 1 1 1))
>>> >>
>>> >> ;; list1 = (1 1 0 1 0 1 1 0)
>>> >> ;; more-lists = ((1 1 0 1 1 1 1 1))
>>> >> ;; lists = ((1 1 0 1 0 1 1 0) (1 1 0 1 1 1 1 1))
>>> >> ;; clozure = #<procedure:...gos-DrRacket.scm:195:11>
>>> >>
>>> >> ;; #f
>>> >> ;;
>>> >> ;;  (function-map-with-escaping-by-kontinuation2
>>> >> (macro-function-compare-2-bits-with-continuation)    '(1 1 0 1 0 1 1
>>> 0) '(1
>>> >> 1 0 1 1 1 1 0))
>>> >>
>>> >> ;; list1 = (1 1 0 1 0 1 1 0)
>>> >> ;; more-lists = ((1 1 0 1 1 1 1 0))
>>> >> ;; lists = ((1 1 0 1 0 1 1 0) (1 1 0 1 1 1 1 0))
>>> >> ;; clozure = #<procedure:...gos-DrRacket.scm:195:11>
>>> >>
>>> >> ;; '(1 1 0 1 x 1 1 0)
>>> >> (define (function-map-with-escaping-by-kontinuation2 clozure list1 .
>>> >> more-lists)
>>> >>    (call/cc (lambda (kontinuation)
>>> >>      (let ((lists (cons list1 more-lists))
>>> >>    (funct-continu ;; this function have the kontinuation in his
>>> environment
>>> >>     (lambda (arg1 . more-args)
>>> >>       (let ((args (cons arg1 more-args)))
>>> >> (apply clozure kontinuation args))))) ;; a tester: (apply clozure
>>> (cons
>>> >> conti args))
>>> >>
>>> >>           ;; (newline)
>>> >>           ;; (dv list1)
>>> >>           ;; (dv more-lists)
>>> >>           ;; (dv lists)
>>> >>   ;; (dv clozure)
>>> >>           ;; (newline)
>>> >>
>>> >>        (apply map funct-continu lists)))))
>>> >>
>>> >> (define-syntax macro-function-compare-2-bits-with-continuation ;;
>>> >> continuation version of macro-compare-2-bits
>>> >>    ;; i need a macro because of external function to the clozure
>>> >>    (syntax-rules ()
>>> >>      ((_) (let ((cnt 0)) ;; counter
>>> >>    (lambda (continuation b1 b2) (if (equal? b1 b2)
>>> >>   b1
>>> >>   (begin
>>> >>     (set! cnt (add1 cnt)) ;; we leave with continuation in case cpt >
>>> 1, we
>>> >> can have used a flag too instead of a counter
>>> >>     (when (> cnt 1) (continuation #f)) ;; escaping with the
>>> continuation
>>> >>     'x))))))) ;; return x in case of (b1,b2) = (O,1) or (1,0)
>>> >>
>>> >> what could have caused mutex if in the latter definition above (let
>>> ((cnt
>>> >> 0)) ;; counter was defined at top level and shared by all threads!!!
>>> yes
>>> >> there could have be some mutex  but this is not the case, i think
>>> even all
>>> >> function are pure so why is it more slow with // than without?
>>> >> Damien
>>> >>
>>> >> On Wed, Oct 12, 2022 at 8:45 PM Maxime Devos <maximedevos@telenet.be>
>>> >> wrote:
>>> >>
>>> >>> On 12-10-2022 19:19, Damien Mattei 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!?
>>> >>>   > [...]
>>> >>>   >
>>> >>>> translated from Scheme+ to Scheme:
>>> >>>> (define unified-minterms-set-1 (map function-unify-minterms-list
>>> >>>> minterms-set)) ;;(par-map function-unify-minterms-list
>>> minterms-set))
>>> >>> The definition of 'function-unify-minterms-list' and 'minterms-set'
>>> is
>>> >>> missing.  Without a test case, we can only speculate what's going on.
>>> >>> (E.g., maybe it grabs a mutex).
>>> >>>
>>> >>> Greetings,
>>> >>> Maxime.
>>> I don't want to scare anyone, just maybe warn about parallel map. I once
>>> tried
>>> to use Guile's parallel map function for a decision tree implementation
>>> (
>>> https://notabug.org/ZelphirKaltstahl/guile-ml/src/cf666801fea91c9fa8fa290764ff6c60b7f3949d/decision-tree.scm),
>>>
>>> where each branch while learning the tree would call parallel map again
>>> for sub
>>> branches and so on. Somehow it made Guile crash (I don't have the error
>>> message
>>> any longer, but I did post about it on the mailing list back then.). I
>>> never
>>> figured out, what went wrong. All I had was pure function calls and math
>>> inside
>>> the thing that parallel map was supposed to run.
>>>
>>> Ultimately I simply tried other parallelism constructs and when I
>>> switched to
>>> using futures instead, everything worked fine, no crashes, no errors.
>>>
>>> Since that time, I did not use parallel map and instead used futures.
>>> Recently I
>>> made a parallelization thing for solving exercises of Project Euler
>>> using
>>> multiple cores, so that some solutions are calculated faster. Maybe this
>>> can
>>> help or can be adapted to another use case:
>>>
>>>
>>> https://notabug.org/ZelphirKaltstahl/guile-project-euler-solutions/src/ebb19b11b465903105924adb6252f1e2ecf63859/lib/parallelism.scm#L11-L30
>>>
>>> It expects ranges of things, which are called `segments` in the code.
>>> Usually
>>> ranges of numbers for Project Euler things. Here is the code to split a
>>> range
>>> into segments:
>>>
>>>
>>> https://notabug.org/ZelphirKaltstahl/guile-project-euler-solutions/src/ebb19b11b465903105924adb6252f1e2ecf63859/lib/segment.scm
>>>
>>> (Check any solution using it for an example.)
>>>
>>> So this might be a bit too specific for general parallel things, but I
>>> guess one
>>> could change the way futures are used in `run-in-parallel`, to fit any
>>> other
>>> purpose.
>>>
>>> Best regards,
>>> Zelphir
>>>
>>> --
>>> repositories: https://notabug.org/ZelphirKaltstahl
>>>
>>>
>>>