RevaMp3D: Architecting the Processor Core and Cache Hierarchy for Systems with Monolithically-Integrated Logic and Memory

TL;DR

RevaMp3D is a novel processor and cache hierarchy design for monolithically integrated 3D memory and logic systems, significantly improving performance and energy efficiency by rethinking cache sharing, latency, and parallelism.

Contribution

It introduces five key architectural changes tailored for M3D systems, including cache removal, latency reduction, pipeline scaling, fine-grained synchronization, and memory-based instruction memoization.

Findings

Achieves 1.2x-2.9x speedup over state-of-the-art M3D systems.

Reduces energy consumption by 1.2x-1.4x.

Provides insights into latency-aware design choices for M3D architectures.

Abstract

Recent nano-technological advances enable the Monolithic 3D (M3D) integration of multiple memory and logic layers in a single chip, allowing for fine-grained connections between layers and significantly alleviating main memory bottlenecks. We show for a variety of workloads, on a state-of-the-art M3D-based system, that the performance and energy bottlenecks shift from main memory to the processor core and cache hierarchy. Therefore, there is a need to revisit current designs that have been conventionally tailored to tackle the memory bottleneck. Based on the insights from our design space exploration, we propose RevaMp3D, introducing five key changes. First, we propose removing the shared last-level cache, as this delivers speedups comparable to or exceeding those from increasing its size or reducing its latency across all workloads. Second, since improving L1 cache latency has a large impact on performance, we reduce L1 latency by leveraging an M3D layout to shorten its wires. Third, we repurpose the area from the removed cache to widen and scale up pipeline structures, accommodating more in-flight requests that are efficiently served by M3D memory. To avoid latency penalties from these larger structures, we leverage M3D layouts. Fourth, to facilitate high thread-level parallelism, we propose a new fine-grained synchronization technique, using M3D's dense inter-layer connectivity. Fifth, we leverage the M3D main memory to mitigate the core bottlenecks. We propose a processor frontend design that memoizes the repetitive fetched, decoded, and reordered instructions, stores them in main memory, and turns off the relevant parts of the core when possible. RevaMp3D provides 1.2x-2.9x speedup and 1.2x-1.4x energy reduction compared to a state-of-the-art M3D system. We also analyze RevaMp3D's design decisions across various memory latencies to facilitate latency-aware design decisions.