Re: Can this type of cache miss be reduced?

Thanks a lot.


I'm looking at the data prefetching. There's an example of loop spliting
in "The compiler Design Handbook"


for (i=0; i<m; i++){
        sum[0] += a[i];
}


===>


for (i=0; i<m; i+=n){
      sum[0] += a[i];
      for(i1 = i+1; i1 < min(m, i+n); i1++){
              sum[0] += a[i1];
      }
}


So we can insert prefetching as


for (i=0; i<m; i+=n){
      prefetch(a[i+pd]);
      sum[0] += a[i];
      for(i1 = i+1; i1 < min(m, i+n); i1++){
              sum[0] += a[i1];
      }
}


I tried this method in my test program. The surprising thing is that the
performance is degrading due to the loop splitting. Even though the data
prefetching can get back some benefit, the overall performance is lower
than before.


Any suggestion?


Cheers
Eric Fisher

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