ZeroCost-LLC: Shared LLCs at No Cost to WCL
Zhuanhao Wu, Anirudh Mohan Kaushik, Hiren Patel · 2023
ZeroCost-LLC (ZCLLC) is a shared inclusive lastlevel cache (LLC) architecture for predictable multicore platforms that does not incur additional cost to the worst-case latency (WCL) of memory requests when compared to the memory hierarchy without an LLC. Thus, the WCL remains the same as without an LLC in the memory hierarchy, but with the performance benefits of having an LLC, in the form of additional caching capacity. ZCLLC achieves this by eliminating all cache line invalidations, and proactively updating the main memory with cache lines to preserve an important vacancy invariant. Furthermore, ZCLLC does not impose any constraints on the way the LLC is used unlike other approaches such as LLC partitioning. Our analysis reveals that the WCL is 55.6%, 68.0%, and 80.2% lower, and the performance is 2.4%, 7.2%, and 25.6% better than the state-of-the-art LLC partition sharing techniques for 2, 4, and 8 cores, respectively.