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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. |
