pLUTo: In-DRAM Lookup Tables to Enable Massively Parallel General-Purpose Computation

Data movement between main memory and the processor is a significant contributor to the execution time and energy consumption of memory-intensive applications. This data movement bottleneck can be alleviated using Processing-in-Memory (PiM), which enables computation inside the memory chip. However, existing PiM architectures often lack support for complex operations, since supporting these operations increases design complexity, chip area, and power consumption. We introduce pLUTo (processing-in-memory with lookup table [LUT] operations), a new DRAM substrate that leverages the high area density of DRAM to enable the massively parallel storing and querying of lookup tables (LUTs). The use of LUTs enables the efficient execution of complex operations in-memory, which has been a long-standing challenge in the domain of PiM. When running a state-of-the-art binary neural network in a single DRAM subarray, pLUTo outperforms the baseline CPU and GPU implementations by $33\times$ and $8\times$, respectively, while simultaneously achieving energy savings of $110\times$ and $80\times$.