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Figure 5.27
Split cache vs. unified cache. |
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Figure 5.28
Design target miss rate of instruction cache (fully associative,
demand fetch, copyback with LRU replacement). |
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ture. The associativity should be adjusted for other caches using the data presented earlier. |
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In certain older program environments, data parameters are frequently placed directly in the program so that when a particular program location is fetched into the I-cache, the same line might also bring data into the I-cache. When the operand parameter is fetched into the D-cache, a duplicate line entry occurs. This appears to happen especially in Fortran programs. Two split-cache policies are possible for dealing with duplicate lines. (See Figure 5.30.) Duplicate lines may be either supported or prohibited. The designer must decide whether enough older programs are expected to be run to warrant the support of duplicate lines. It has been shown that in these older environments, cache performance significantly degrades when a "no-duplicate-line" policy is adopted. In more modern programming envi- |
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