Slow memory access

[tofuny]

Hi!!, I have to access the array p in loop of k index of below code to save any calculated value. But it takes much time to access the array. I checked access time in my machine (VS2008, release mode, i7(6 cores), windows 7):

- there is empty loop(no calculation and no array access): 17ms

- there is the calculation part of (1): 17ms

- no calculation part and there is just "p = 1000" in the loop : 21ms

- calculation part (1) + "p = 1000" : 57ms

- calculation part (1) + "p = val" : 123ms

I cannot understand why it takes so long time to access the array "p" in the for loop.

=======================================

#include "tbb/tbb.h"

#include "tbb/blocked_range.h"

#include "tbb/blocked_range2d.h"

#include "tbb/parallel_for.h"

#include "tbb/tick_count.h"

#include "tbb/scalable_allocator.h"

using namespace std;

using namespace tbb;

/////

class Average : public CPartLoop

{

public:

...

int hh, ww;

void operator() (const blocked_range2d& range) const;

void ParallelProcessing(int hh, int ww);

};

void Average::operator() (const blocked_range2d& range) const

{

register int i,j,k;

float *p = scalable_allocator().allocate(100);

for(i=range.rows().begin(); i != range.rows().end(); ++i)

{

int ii = (int)(i/50);

int jj = i-ii*50;

for(j=range.cols().begin(); j != range.cols().end(); ++j)

{

int dd = (int)(j/36);

int ss = j-dd*36;

for(k=0; k

{

//// (1) math calculation part ////

int nr = (int)kp.r;

int nc = (int)kp.c;

if( ii+nr>hh-1 || ii+nr<0 || jj+nc > ww-1 || jj+nc<0) continue;

int index1 = (ii+nr)*ww;

int tr = A[index1+(jj+nc)];

int tc = B[index1+(jj+nc)];

float te = C[index1+(jj+nc)];

float aa = dd + (kp.d*r2d);

float bb = kp.e;

float val = (tr+tc)*cos(aa*d2r)*(bb * te);

////// end of (1) ///////

p = val; // 1000 // (2) array access part

}

}

}

tbb::scalable_allocator().deallocate(p,100);

}

void Average::ParallelProcessing(int hh, int ww)

{

this->hh = hh;

this->ww = ww;

parallel_for(blocked_range2d(0,50*50,4,0,360,4), *this);

}

[RafSchietekat]

Before we look at anything else, try to "hoist" the range boundary "out of the loop" (just in the inner loop may well be enough), by assigning it to a value that can then be used in the condition instead. The compiler may then be able to perform better optimisations.

(Added 2012-04-03) Well, maybe not here...

[SergeyKostrov]

Could you provide a complete Test-Case? Here is a list of compilation errors:

...
error C2504: 'CPartLoop' : base class undefined
error C2065: 'kp' : undeclared identifier
error C2065: 'A' : undeclared identifier
error C2065: 'B' : undeclared identifier
error C2065: 'C' : undeclared identifier
error C2065: 'r2d' : undeclared identifier
error C2065: 'd2r' : undeclared identifier
...