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Show simulation. A random pattern of accesses to the main memory is present, but more computation is done for each item than in the N-queens program. It is expected that the scientific simulation exhibits an average case performance of the history cache for complex interactive programs. These two programs were chosen, because they access the memory at random and because they can be scaled linearly in memory size and in the number of executed instructions. Measurements do not include the routines from the operating system and the standard library. Numerous parameters of the history cache were varied in measurements. The replacement policy used in all measurements is last recently used (LRU). When an item is removed from the history cache, the LRU replacement policy removes the item that has not been referenced for the longest time. Results for other replacement policies are not shown since the measurements show that the replacement policy has only a limited effect on the history cache performance. Measurements do not include the small storage overhead of processor state. The history cache was flushed every 1,000,000 executed instructions. Since the history cache is word oriented with 32-bit words, a line size is never less than four bytes. Several measurements were performed. First, the number of cache entries was varied for a fully associative cache organization. Second, the line size and the number of sets were varied in a history cache for a fixed cache size. Third, the problem size was varied for a fixed cache organization. Number of Cache Entries The compaction in the history depending on the number of history cache entries was measured for a fully associative cache with an LRU replacement strategy. The number of entries was increased in powers of 2 from 2° to 213 words (see Figure 5.12). Since a large portion of the N-queens program is spent in initialization, two statistics are given for the N-queens program: for the entire program and for the part of the program without the initialization. The History Ratio shows 141 |
