Dynamic associativity management using fellow sets

The memory accesses of todays applications are non-uniformly distributed across the cache sets and as a result some sets of the cache are heavily used while some other sets remain underutilized. This paper presents CMP-SVR, an approach to dynamically increase the associativity of heavily used sets without increasing the cache size. It divides the last level cache (LLC) into two sections: normal storage (NT) and reserve storage (RT). Some number of ways (25% to 50%) from each set are reserved for RT and the remaining ways belongs to NT. The sets are divided into some groups called fellow-groups and a set can use the reserve ways of its fellow sets to increase its associativity during execution. An additional tag-array (SA-TGS) for RT has been used to make the searching easier and less expensive. SA-TGS is almost like an N-way set associative cache where its associativity depends on the number of reserve ways per set and the number of sets in a fellow-group. CMP-SVR has less storage, area and energy overhead as compared to the other techniques proposed for dynamic associativity management. Full system simulation shows on average of 8% improvement in cycles per instruction (CPI) and 28% improvement in miss-rate.