...

Now interchange so blocked loops are outermost:

for (kk = 0; kk < 500; kk += BLKSZ)
 for (jj = 0; jj < 500; jj += BLKSZ)
  for (i = 0; i < 500; i++)
   for (k = kk; k < min(kk+BLKSZ,500); k++){
    r = A[i][k];
     for (j = jj; j < min(jj+BLKSZ, 500); j++)
      C[i][j] += r * B[k][j];
    }

• The inner i,k,j loops perform a multiplication of a pair of partial matrices.
• BLKSZ is chosen so that a submatrix of B and a row of length BLKSZ of C can fit in the cache.
• What is the right value for BLKSZ?