Perfomance slowdown with growth of operations number

I have next problem. My code performance depends on number of operation! How can it be? (I use gcc v 4.3.2 under openSuse 11.1)

Here is my code:

#define N_MAX 1000000

typedef unsigned int uint;

double  a[N_MAX];
double  b[N_MAX];
uint n;

int main(){


    for (uint i=0; i<N_MAX; i++) {
            a[i]=(double)rand()/RAND_MAX;
    }


    for (uint n=100000; n<500000; n+=5000) {

        uint time1 = time(NULL);

        for (uint i=0; i<n;++i)
            for (uint j=0;j<n;++j)
                    b[j] = a[j]; 

        uint time2 = time(NULL);

        double time = double(time2-time1);

        printf("%5d ", n);
        printf("%5.2f %.3f\n", time, ((double)n*n/time)/1e9);

    }

    return 0;
}

And here is the log of results:

n-time-Gflops (=)

200000 23.00 1.739

205000 24.00 1.751

210000 25.00 1.764

215000 26.00 1.778

220000 27.00 1.793

225000 29.00 1.746

230000 30.00 1.763

235000 32.00 1.726

240000 32.00 1.800

245000 34.00 1.765

250000 36.00 1.736

255000 37.00 1.757

260000 38.00 1.779

265000 40.00 1.756

270000 42.00 1.736

275000 44.00 1.719

280000 46.00 1.704

285000 48.00 1.692

290000 49.00 1.716

295000 51.00 1.706

300000 54.00 1.667

305000 54.00 1.723

310000 59.00 1.629

315000 61.00 1.627

320000 66.00 1.552

325000 71.00 1.488

330000 76.00 1.433

335000 79.00 1.421

340000 84.00 1.376

345000 85.00 1.400

350000 89.00 1.376

355000 96.00 1.313

360000 102.00 1.271

365000 110.00 1.211

370000 121.00 1.131

375000 143.00 0.983

380000 156.00 0.926

385000 163.00 0.909

There is also the image but I can't post it cause of new users restrictions. But here is the log plot.

What is the reason of开发者_StackOverflow社区 this slowdown? How to get rid of it? Please Help!

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Your inner loops increase number of iterations every time - it is expected to take more time to do their job if there is more calculations to do. First time there are 100k operations to be done, second time 105k operations, and so on. It simply must take more and more time.

EDIT: To be clearer, I tried to say it looks to something that Spolsky called Shlemiel the painter's algorithm

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Thank a lot for response!

My expectation bases on idea that operation number per time unit should remains the same. So if I increase number of operations, say twice, then computation time should increase also twice, therefore the ration of operations number and the computation time should be constant. This is something that i didn't meet. :(