U-Cache: A Cost-Effective Solution to the Synonym Problem

This paper proposes a cost-eeective solution to the synonym problem. In this proposed solution, a minimal hardware addition guarantees the correctness whereas the software counterpart helps improve the performance. The key to this proposed solution is an addition of a small physically-indexed cache called U-cache. The U-cache maintains the reverse translation information of the cache blocks that belong to un-aligned virtual pages only, where aligned means that the lower bits of the virtual page number match those of the corresponding physical page number. A U-cache, even with only one entry, ensures correct handling of synonyms. A simple software optimization, in the form of page alignment, helps improve the performance. Performance evaluation based on ATUM traces shows that a U-cache, with only a few entries, performs almost as well as (in some cases outperforms) a fully-conngured hardware-based solution when more than 95 % of the pages are aligned.