[racket] Small and short-lived data structures

Strange results. I did some benchmarks.
The 'mcons solution use always the same mcon to return the results of
all the function calls. It’s different from the 'cons solution that
returns a different con in each function call. I made a new version:
loop4 (see code bellow).

I ran the program 10 times, with different values of K = 10^5, 10^6,
10^7 and 10^8. This table has the cpu time: average ± stdev, ordered
by K=1E8.

Method           K=1E5        K=1E6          K=1E7           K=1E8
'0-direct         7.8±8.2    137.5± 9.7    1434.4±35.2    13940.4±59.2
'3-mcons-one      9.5±8.2    151.4±14.8    1424.9± 9.7    14262.9±56.1
'4-mcons-diff    10.9±7.5    151.7±13.1    1442.2±10.4    14474.8±44.5
'1-cons          12.5±6.6    145.3± 7.6    1509.3±39.7    14582.7±72.1
'2-values         9.4±8.1    167.2± 7.7    1610.9±11.5    16117.4±47.8

With K=1E8 the results differences are significant. The faster
versions are the '0-direct and '3-mcons-one (old version). They don’t
allocate a new con or mcon in each cicle. The slowest versions is
'2-values, in my experience values are very slow in Racket.

I’m still surprised that '4-mcons-diff is faster than '1-cons. The
code is identical and the only difference is that one uses mcon and
the other uses con.

Gustavo

;-------------------------
(begin-encourage-inline
 (define (f4 x y)
   (mcons (+ x y) (- x y)))

 (define (g4 x)
   (+ (unsafe-mcar x) (unsafe-mcdr x))))

(define (loop4 n)
  (for/sum ([i (in-range n)])
    (g4 (f4 i (unsafe-fx+ 1 i)))))
;-------------------------

On Mon, Oct 21, 2013 at 3:43 PM, Sam Tobin-Hochstadt
<samth at cs.indiana.edu> wrote:
> I encourage you to find some evidence showing that Konrad's assumption
> is mistaken, then.
>
> Sam
>
> On Mon, Oct 21, 2013 at 2:38 PM, Matthias Felleisen
> <matthias at ccs.neu.edu> wrote:
>>
>> WIth respect, I think this shows nothing :-)
>>
>>
>>
>> On Oct 21, 2013, at 2:35 PM, Sam Tobin-Hochstadt <samth at cs.indiana.edu> wrote:
>>
>>> On Mon, Oct 21, 2013 at 12:47 PM, Matthias Felleisen
>>> <matthias at ccs.neu.edu> wrote:
>>>>
>>>> In general, it is a mistaken assumption however that even in a
>>>> 'managed' language -- such as Java or Racket -- mutation is still
>>>> faster than de/allocation of short-lived data structures. If you
>>>> choose to go with 'managed' language, you need to adapt your
>>>> programming style to the new context.
>>>
>>> Sadly, this assumption is often right for Racket today, even though we
>>> have a pretty good allocator.  Here's a simple benchmark:
>>> https://gist.github.com/samth/7088570
>>>
>>> This just passes multiple arguments between two functions in three
>>> ways: with a cons, with multiple values, and by mutating an mcons
>>> (plus a direct version with two local variables).  In all cases, it's
>>> as fast as I can make it, using unsafe operations where appropriate.
>>>
>>> Here are some representative timings:
>>>
>>> [samth at huor:~/sw/plt/racket/collects/racket/match (master) plt] r /tmp/bench.rkt
>>> 'direct
>>> cpu time: 40 real time: 44 gc time: 0
>>> 'cons
>>> cpu time: 72 real time: 73 gc time: 12
>>> 'values
>>> cpu time: 192 real time: 191 gc time: 0
>>> 'mcons
>>> cpu time: 48 real time: 51 gc time: 0
>>>
>>> Direct is always fastest, multiple values are very slow, and cons is
>>> always slower than mcons.  Even if we ignore GC time, the functional
>>> version is still always slower.
>>>
>>> Sam
>>
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