  Neural networks (NNs) are growing in importance and complexity. A neural
network's performance (and energy efficiency) can be bound either by
computation or memory resources. The processing-in-memory (PIM) paradigm, where
computation is placed near or within memory arrays, is a viable solution to
accelerate memory-bound NNs. However, PIM architectures vary in form, where
different PIM approaches lead to different trade-offs. Our goal is to analyze,
discuss, and contrast DRAM-based PIM architectures for NN performance and
energy efficiency. To do so, we analyze three state-of-the-art PIM
architectures: (1) UPMEM, which integrates processors and DRAM arrays into a
single 2D chip; (2) Mensa, a 3D-stack-based PIM architecture tailored for edge
devices; and (3) SIMDRAM, which uses the analog principles of DRAM to execute
bit-serial operations. Our analysis reveals that PIM greatly benefits
memory-bound NNs: (1) UPMEM provides 23x the performance of a high-end GPU when
the GPU requires memory oversubscription for a general matrix-vector
multiplication kernel; (2) Mensa improves energy efficiency and throughput by
3.0x and 3.1x over the Google Edge TPU for 24 Google edge NN models; and (3)
SIMDRAM outperforms a CPU/GPU by 16.7x/1.4x for three binary NNs. We conclude
that the ideal PIM architecture for NN models depends on a model's distinct
attributes, due to the inherent architectural design choices.
