METHOD AND CACHE SYSTEM WITH SOFT I-MRU MEMBER PROTECTION SCHEME DURING MAKE MRU ALLOCATION

A caching mechanism implementing a “soft” Instruction-Most Recently Used (I-MRU) protection scheme whereby the selected I-MRU member (cache line) is only protected for a limited number of eviction cycles unless that member is updated/utilized during the period. An update or access to the instruction restarts the countdown that determines when the cache line is no longer protected as the I-MRU. Accordingly, only frequently used Instruction lines are protected, and old I-MRU lines age out of the cache. The old I-MRU members are evicted, such that all the members of a congruence class may be used for data. The I-MRU aging is accomplished through a counter or a linear feedback shift register (LFSR)-based “shootdown” of I-MRU cache lines. The LFSR is tuned such that an I-MRU line will be protected for a pre-established number of evictions.