This paper proposes a cost-effective solution to the synonym problem of virtual caches. In the 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 unaligned virtual pages only, where aligned measns that the lower bits of the virtual page number match those of the corresponding physical page number. The page alignment is a simple software optimization to improve the performance of the U-cche hardware. With the combination of both hardware and software, the proposed solution reduces the hardware costs and minimizes software modification and performance degradation. Performance evaluation base on ATUM traces shows that a U-cache, with only a few entries, performs almost as well as fully-configured hardware-based solution when more than 95% of the pages are aligned.
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