Is it possible to lock some data in CPU cache?

Question

I have a problem.... I'm writing a data into array in the while-loop. And the point is that I'm doing it really frequently. It seems to be that this writing is now a bottle-neck in the code. So as i presume it's caused by the writing to memory. This array is not really large (smth like 300 elements). The question is it possible to do it in that way: to store it in the cache and update in the memory only after the while-loop is finished?

[edit - copied from an answer added by Alex]

double* array1  = new double[1000000]; // this array has elements  
unsigned long* array2  = unsigned long[300];
double varX,t,sum=0;
int iter=0,i=0;
while(i<=max_steps)
{
   varX+=difX;
   nm0 =  int(varX);
   if(nm1!=nm0)
   {
        array2[iter] = nm0;  // if you comment this string application works more then 2 times faster :)
        nm1=nm0;
        t = array1[nm0]; // if you comment this string , there is almost no change in time 
        ++iter;
   }
   sum+=t;
   ++i;
}

---

For the first I'd like to thank all of you for answers. Indeed, it was a little dumb not to place a code. So i decided to do it now.

double* array1  = new double[1000000]; // this array has elements  
unsigned long* array2  = unsigned long[300];
double varX,t,sum=0;
int iter=0,i=0;
while(i<=max_steps)
{
   varX+=difX;
   nm0 =  int(varX);
   if(nm1!=nm0)
   {
        array2[iter] = nm0;  // if you comment this string application works more then 2 times faster :)
        nm1=nm0;
        t = array1[nm0]; // if you comment this string , there is almost no change in time 
        ++iter;
   }
   sum+=t;
   ++i;
}

So that was it. It would be nice if someone will have any ideas. Thank you very much again.

Sincerely Alex

Answer 1

Not intentionally, no. Among other things, you have no idea how big the cache is, so you have no idea of what's going to fit. Furthermore, if the app were allowed to lock off part of the cache, the effects on the OS might be devastating to overall system performance. This falls squarely onto my list of "you can't do it because you shouldn't do it. Ever."

What you can do is to improve your locality of reference - try to arrange the loop such that you don't access the elements more than once, and try to access them in order in memory.

Without more clues about your application, I don't think more specific advice can be given.