Mapping Choices in Hierarchy
Tradeoff cost of miss vs cost of associativity.
VM uses fully associative mapping
- Reduces miss rate, because miss penalty is high
- Mapping done in software
- Large page size means page table size overhead is small
- Note that page table is indexed, but full map provides fully associative placement
Small caches (TLB) often use set associative placement
Large caches never use fully associative placement
- High cost and hit time penalties
- Small performance advantage to set associative