… a fundamental characteristic of complex human systems … [is that] cause and effect are not close in time and space. By effects, I mean the obvious symptoms that indicate that there are problems drug abuse, unemployment, starving children, falling orders, and sagging profits. By cause I mean the interaction of the underlying system that is most responsible for generating the symptoms, and which, if recognized, could lead to changes producing lasting improvement. Why is this a problem? Because most of us assume they are most of us assume, most of the time, that cause and effect are close in time and space.

Focus your attention on the inner loops, where the bulk of the computationsand memory accesses occur.. Try to maximize the spatial locality in your programs by reading data objectssequentially, with stride 1, in the order they are stored in memory.. Try to maximize the temporal locality in your programs by using a data objectas often as possible once it has been read from memory.

Programs that repeatedly reference the same variables enjoy good temporallocality..For programs with stride-k reference patterns, the smaller the stride, thebetter the spatial locality. Programs with stride-1 reference patterns have goodspatial locality. Programs that hop around memory with large strides havepoor spatial locality..Loops have good temporal and spatial locality with respect to instructionfetches. The smaller the loop body and the greater the number of loop it-erations, the better the locality.

Visiting every kth element of a contiguous vector is called a stride-kreference pattern. Stride-1 reference patterns are a common and important sourceof spatial locality in programs. In general, as the stride increases, the spatial localitydecreases.