Bicameral+ Cache: re-assessing split vector and scalar cache designs for increased efficiency

Abstract Addressing the growing impact of the memory wall is critical to sustain performance in modern vector architectures. This work introduces the Bicameral+ Cache, an enhanced version of the Bicameral Cache architecture, which separates scalar and vector memory accesses into distinct cache structures, optimized for their respective locality patterns. Bicameral+ Cache incorporates two key improvements: a transition from a fully associative to a set-associative organization in the vector cache, reducing implementation complexity while preserving performance, and a novel replacement policy based on a configurable write-back threshold (WBT), which improves memory traffic efficiency. Experimental results show speedups of up to 1.59 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> in dense workloads and 1.63 $$\times $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>×</mml:mo> </mml:math> in sparse ones, with respect to a conventional cache, when using a 16-way set-associative Bicameral+ Cache configuration. These findings, combined with estimations of a sevenfold area reduction and energy savings of one order of magnitude, confirm the practicality and effectiveness of the proposed enhancements for vector processing systems, retaining the benefits of the original Bicameral Cache design at reduced complexity and implementation costs.