[racket] Places performance

As Robby said, the time should only include both place-channel-get and  
-put calls to make it comparable.
But this is not enough, because the (place ...)-creation seems to be  
non-blocking, i.e they might not be started up yet when the codes reached  
the first -put.

This can be solved by explicitly synchronizing the places with the main  
program:

(define (places-main)
     (define place1
        (place ch
               (begin
                 (place-channel-put ch #t)
                 (place-channel-put ch (test-function (place-channel-get  
ch))))))

     (define place2
         (place ch
                (begin
                  (place-channel-put ch #t)
                  (place-channel-put ch (test-function (place-channel-get  
ch))))))

     (place-channel-get place1)
     (place-channel-get place2)

     (display "With places ")
     (time
      (place-channel-put place1 test-vector)
      (place-channel-put place2 test-vector)
      (place-channel-get place1)
      (place-channel-get place2))
     (place-wait place1)
     (place-wait place2)
     (void))


With this i get the following times

With places cpu time: 5600 real time: 3199 gc time: 404
Without places cpu time: 3700 real time: 3678 gc time: 2208

Now its at least faster than the sequential version. But the overhead  
seems to be still a lot more than i had expected.

Tobias



On Thu, 14 Mar 2013 02:23:22 +0100, Harry Spier  
<vasishtha.spier at gmail.com> wrote:

> Dear members,
>
> I've run the following racket program  (as an executable) to test the
> performance of places on a windows dual core pentium machine under Vista.
>  I've run this with various sizes for test-vector.  Even when the amount  
> of
> computation is large (test-vector-size = 5000000) the performance with  
> the
> computation split over two places takes more than double the time to
> complete as when no places are used.
>
> I'm not clear why on a dual core machine the performance wasn't better  
> with
>  the computation split over two places than with no places. In fact the
> results are the opposite with the performance for no places always double
> that for two places.
>
> --------------------------------------
> place-timing-test-executable.rkt
> ---------------------------------------
> #lang racket
> (require "place-timing-test.rkt")
> (printf "test-vector-size ~a" test-vector-size)
> (newline)
> (display "With places ")
> (time (places-main))
> (display "Without places ")
> (time (noplaces-main))
>
> (system "PAUSE")
>
>
> -----------------------
> place-timing-test.rkt
> -----------------------
> #lang racket
> (provide places-main noplaces-main test-vector-size)
> (define test-vector (build-vector 5000000 +))
> (define test-vector-size (vector-length test-vector))
> (define (test-function vectr) (apply + (vector->list (vector-map sqrt
> vectr))))
>
> (define (places-main)
>     (define place1
>        (place ch (place-channel-put ch (test-function (place-channel-get
> ch)))))
>
>     (define place2
>         (place ch (place-channel-put ch (test-function (place-channel-get
> ch)))))
>
>     (place-channel-put place1 test-vector)
>     (place-channel-put place2 test-vector)
>     (place-channel-get place1)
>     (place-channel-get place2)
>     (place-wait place1)
>     (place-wait place2)
>     (void))
>
> (define (noplaces-main)
>     (test-function test-vector)
>     (test-function test-vector)
>     (void)
> -------------------------------
>
> These are the results for different sizes of test-vector.  The amount of
> computation is linear to the size of test-vector.
>
> test-vector-size 100000
> With places cpu time: 1685 real time: 856 gc time: 0
> Without places cpu time: 187 real time: 170 gc time: 94
> Press any key to continue . . .
> -----
> test-vector-size 1000000
> With places cpu time: 3822 real time: 2637 gc time: 265
> Without places cpu time: 1201 real time: 1191 gc time: 452
> Press any key to continue . . .
> -------
> test-vector-size 5000000
> With places cpu time: 15787 real time: 23318 gc time: 1373
> Without places cpu time: 7769 real time: 9456 gc time: 4461
> Press any key to continue . . .
> ------
>
> Thanks,
> Harry Spier


-- 
---------------------------------------------------------
Tobias Hammer
DLR / Institute of Robotics and Mechatronics
Muenchner Str. 20, D-82234 Wessling
Tel.: 08153/28-1487
Mail: tobias.hammer at dlr.de