ASPEN: A Scalable In-SRAM Architecture for Pushdown Automata

Many applications process some form of tree-structured or recursively-nested data, such as parsing XML or JSON web content as well as various data mining tasks. Typical CPU processing solutions are hindered by branch misprediction penalties while attempting to reconstruct nested structures and also by irregular memory access patterns. Recent work has demonstrated improved performance for many data processing applications through memory-centric automata processing engines. Unfortunately, these architectures do not support a computational model rich enough for tasks such as XML parsing. In this paper, we present ASPEN, a general-purpose, scalable, and reconfigurable memory-centric architecture for processing of tree-like data. We take inspiration from previous automata processing architectures, but support the richer deterministic pushdown automata computational model. We propose a custom datapath capable of performing the state matching, stack manipulation, and transition routing operations of pushdown automata, all efficiently stored and computed in memory arrays. Further, we present compilation algorithms for transforming large classes of existing grammars to pushdown automata executable on ASPEN, and demonstrate their effectiveness on four different languages: Cool (object oriented programming), DOT (graph visualization), JSON, and XML. Finally, we present an empirical evaluation of two application scenarios for ASPEN: XML parsing, and frequent subtree mining. The proposed architecture achieves an average 704.5 ns per KB parsing XML compared to 9983 ns per KB in a state-of-the-art XML parser across 23 benchmarks. We also demonstrate a 37.2x and 6x better end-to-end speedup over CPU and GPU implementations of subtree mining.