Re: Old problem with performance

[Denis Koroskin]

On Sun, 08 Feb 2009 20:24:08 +0300, naryl <c...@ngs.ru> wrote:

Denis Koroskin Wrote:

On Sun, 08 Feb 2009 18:40:53 +0300, Denis Koroskin <2kor...@gmail.com> wrote:

> On Sun, 08 Feb 2009 18:09:41 +0300, naryl <c...@ngs.ru> wrote:
>
>> It's a bit offtopic but I'd be grateful if someone can explain why D

>> with structs completes this simple benchmark (see attachment) so slowly

>> compared to C++ with classes on stack:
>>
>> D struct - 27.85s
>> C++ stack - 8.32s
>>
>> D class - 271.58s
>> C++ heap - 249.32s
>>
>> Compiled with "dmd -O". -release decreases performance by 10% in this
>> case. -inline doesn't affects it at all.
>
> I noticed that you calculate Fib(27) in fibs.cc and Fib(40) in fibs.d
> Can this affect such a big difference between C++ and D version?
>

They both perform roughly the same when this typo is corrected.

Sorry. :)

For n=40 I get:
C++ compiled with "g++ -O fibs.cc" - 5.37s
D compiled with "dmd -O -inline fibs.d" - 14.32s
D compiled with "dmd -O -inline -release fibs.d" - 15.20s

DMD 2.023 is still almost three times slower.

Here is code, setting and result I got.

D version:

import std.stdio;

extern(Windows) int timeGetTime();

struct Fib {
        private int _value;

        int value() {
                if(_value <= 2)
                        return 1;

                scope f1 = Fib(_value - 1);
                scope f2 = Fib(_value - 2);

                return f1.value() + f2.value();
        }
}

void main()
{
        int start = timeGetTime();
        
        int value = 0;

        foreach (i; 0 .. 10) {
                value += Fib(40).value;
        }
        
        int stop = timeGetTime();

        writefln(value);
        writefln("Time elapsed: %s", stop - start);
}

C++ version:


#include <stdio.h>
#include <windows.h>

class Fib
{
        private:
                int _value;

        public:
                Fib(int n) { _value = n; }

                int value()
                {
                        if(_value <= 2)
                                return 1;

                        Fib f1 = Fib(_value - 1);
                        Fib f2 = Fib(_value - 2);

                        return f1.value() + f2.value();
                }
};

int main()
{
        int start = timeGetTime();
        
        int value = 0;

        for(int i=0; i<10; i++)
        {
                Fib x = Fib(40);
                value += x.value();
        }
        
        int stop = timeGetTime();
        
        printf("%d\n", value);
        printf("Time elapsed: %d\n", stop - start);

        return 0;
}

And here are results (best/average of 3 runs):

DMD2.023 - 12.492/12.576 ms (-O -inline)
DMC8.42n - 13.941/14.131 ms (-O -inline)