LLC Intra-set Write Balancing

TL;DR

This paper introduces a sample-based blocking technique for LLC in NVM systems to balance write traffic, reduce cell degradation, and extend memory lifespan without sacrificing performance.

Contribution

It proposes a novel sampling and history-based blocking method for LLC to improve write endurance in NVM, adaptable to various cache hierarchies.

Findings

Significantly balances write traffic in LLC.

Improves memory cell lifespan.

Maintains or improves system performance.

Abstract

The increasing use of Non-Volatile Memory (NVM) in computer architecture has brought about new challenges, one of which is the write endurance problem. Frequent writes to a particular cache cell in NVM can lead to degradation of the memory cell and reduce its lifespan. To solve this problem, we propose a sample-based blocking technique for the Last Level Cache (LLC). Our approach involves defining a threshold value and sampling a subset of cache sets. If the number of writes to a way in a sampled set exceeds the threshold, the way is blocked, and writes are redirected to other ways. We also maintain a history structure to record the number of writes in a set and a PC-Table to use for blocking in unsampled sets. Based on blocking on sampled sets, variance of values stored in history is used to determine whether blocking had a positive impact or not, and on this basis, value corresponding to instruction pointer is incremented or decremented. This value is later used for blocking in unsampled sets. Our results show that our approach significantly balances write traffic to the cache and improves the overall lifespan of the memory cells while having better performance to the base-line system. Our approach can also be applied to other cache hierarchies and NVM technologies to mitigate the problem of write endurance.