# HoLiSwap: Reducing Wire Energy in L1 Caches

## TL;DR

HoLiSwap is a technique that reduces L1 cache wire energy by dynamically swapping hot cache lines to the nearest way, achieving significant energy savings without impacting cache performance.

## Contribution

It introduces a novel method to identify and swap hot cache lines to reduce wire energy, improving efficiency in set-associative L1 caches.

## Key findings

- Up to 44% wire energy reduction
- 0.13% system energy savings
- No impact on cache miss rate or performance

## Abstract

This paper describes HoLiSwap a method to reduce L1 cache wire energy, a significant fraction of total cache energy, by swapping hot lines to the cache way nearest to the processor. We observe that (i) a small fraction (<3%) of cache lines (hot lines) serve over 60% of the L1 cache accesses and (ii) the difference in wire energy between the nearest and farthest cache subarray can be over 6$\times$. Our method exploits this difference in wire energy to dynamically identify hot lines and swap them to the nearest physical way in a set-associative L1 cache. This provides up to 44% improvement in the wire energy (1.82% saving in overall system energy) with no impact on the cache miss rate and 0.13% performance drop. We also show that HoLiSwap can simplify way-prediction.