There has been a resurgence of interest in vector architectures evident by recent adoption of vector extensions in mainstream instruction set architectures. Traditionally, vector engines leverage this abstraction by exploiting its inherent regularity to increase performance and efficiency. Recent work on SRAM-based compute-in-memory has shown promise in reducing the area overhead of these engines. In this work, we propose ephemeral vector engines (EVE) where we leverage SRAM-based compute-in-memory techniquesas well as bit-peripheral computations to facilitate efficient vector execution. EVE uses a novel approach of bit-hybrid execution, striking a balance between throughput and latency. Evaluated on the Rodinia and RiVEC benchmark suites, EVE achieves almost 8× speed-up compared to an out-of-order processor and 4.59× compared to an integrated vector unit. EVE achieves speed-ups comparable to an aggressive decoupled vector unit and increases the area-normalized performance by over 2 ×. By repurposing SRAM arrays in the L2 cache to create ephemeral vector execution units, EVE is able to efficiently achieve high performance while incurring as little as 11.7% area overhead.

Single-ISA heterogeneous multi-core architectures offer a compelling high-performance and high-efficiency solution to executing task-parallel workloads in mobile systems on chip (SoCs). In addition to task-parallel workloads, many data-parallel applications, such as machine learning, computer vision, and data analytics, increasingly run on mobile SoCs to provide real-time user interactions. Next-generation scalable vector architectures, such as the RISC-V Vector Extension and Arm SVE, have recently emerged as unified vector abstractions for both large- and small-scale systems. In this paper, we propose novel area-efficient high-performance architectures called big.VLITTLE that support next-generation vector architectures to efficiently accelerate data-parallel workloads in conventional big.LITTLE systems. big.VLITTLE architectures reconFigure multiple little cores on demand to work as a decoupled vector engine when executing data-parallel workloads. Our results show that a big.VLITTLE system can achieve $1.6\times$ performance speedup over an area-comparable big.LITTLE system equipped with an integrated vector unit across multiple data-parallel applications and $1.7\times$ speedup compared to an aggressive decoupled vector engine for task-parallel workloads.

Processing-in-memory (PIM) architectures attempt to overcome the von Neumann bottleneck by combining computation and storage logic into a single component. The content-addressable parallel processing paradigm (CAPP) from the seventies is an in-situ PIM architecture that leverages content-addressable memories to realize bit-serial arithmetic and logic operations, via sequences of search and update operations over multiple memory rows in parallel. In this paper, we set out to investigate whether the concepts behind classic CAPP can be used successfully to build an entirely CMOS-based, general-purpose microarchitecture that can deliver manyfold speedups while remaining highly programmable. We conduct a full-stack design of a Content-Addressable Processing Engine (CAPE), built out of dense push-rule 6T SRAM arrays. CAPE is programmable using the RISC-V ISA with standard vector extensions. Our experiments show that CAPE achieves an average speedup of 14 (up to 254) over an area-equivalent (slightly under 9 mm2at 7 nm) out-of-order processor core with three levels of caches.

Vector accelerators can efficiently execute regular data-parallel workloads, but they require expensive multi-ported register files to feed large vector ALUs. Recent work on in-situ processing-in-SRAM shows promise in enabling area-efficient vector acceleration. This work explores two different approaches to leveraging in-situ processing-in-SRAM: BS-VRAM, which uses bit-serial execution, and BP-VRAM, which uses bit-parallel execution. The two approaches have very different latency vs. throughput trade-offs. BS-VRAM requires more cycles per operation, but is able to execute thousands of operations in parallel, while BP-VRAM requires fewer cycles per operation, but can only execute hundreds of operations in parallel. This paper is the first work to perform a rigorous evaluation of bit-serial vs. bit-parallel in-situ processing-in-SRAM. Our results show that both approaches have similar area overheads. For 32-bit arithmetic operations, BS-VRAM improves throughput by 1.3-5.0× compared to BP-VRAM, while BP-VRAM improves latency by 3.0-23.0× compared to BS-VRAM.

Task-based parallel programming frameworks offer compelling productivity and performance benefits for modern chip multi-processors (CMPs). At the same time, CMPs also provide packed-SIMD units to exploit fine-grain data parallelism. Two fundamental challenges make using packed-SIMD units with task-parallel programs particularly difficult: (1) the intra-core parallel abstraction gap; and (2) inefficient execution of irregular tasks. To address these challenges, we propose augmenting CMPs with intra-core loop-task accelerators (LTAs). We introduce a lightweight hint in the instruction set to elegantly encode loop-task execution and an LTA microarchitectural template that can be configured at design time for different amounts of spatial/temporal decoupling to efficiently execute both regular and irregular loop tasks. Compared to an in-order CMP baseline, CMP+LTA results in an average speedup of 4.2X (1.8X area normalized) and similar energy efficiency. Compared to an out-of-order CMP baseline, CMP+LTA results in an average speedup of 2.3X (1.5X area normalized) and also improves energy efficiency by 3.2X. Our work suggests augmenting CMPs with lightweight LTAs can improve performance and efficiency on both regular and irregular loop-task parallel programs with minimal software changes.