AxBA: An Approximate Bus Architecture Framework

Modern computing platforms expend significant amounts of time and energy in transmitting data across on-chip and off-chip interconnects. This challenge is exacerbated in prevalent data-intensive workloads such as machine learning, data analytics and search. However, these workloads also present a unique opportunity in the form of intrinsic resilience to approximations in computations and data. We explore approximate compression of communication traffic, which leverages this intrinsic resilience to improve communication bandwidth and reduce the energy consumed by interconnects. Specifically, we propose AxBA, an approximate bus architecture framework that is aware of the data amenable to approximations and seamlessly compresses/decompresses the corresponding transactions on the bus without requiring any changes to pre-designed masters and slaves. AxBA uses a lightweight compression scheme based on approximate deduplication, which is suitable for the tight latency constraints imposed by bus-based interconnects. To facilitate software development on AxBA-based systems, we introduce a software interface that enables programmers to identify regions of the system address space that are amenable to approximations. We also propose a run-time quality monitoring framework that automatically determines the error constraints for the identified regions such that a specified application-level quality is maintained. We demonstrate the feasibility of the proposed concepts by realizing a prototype AxBA system on a Cyclone-IV FPGA development board using an Intel Nios II processor-based SoC. Across a suite of six machine learning benchmarks, AxBA obtains an average improvement in system performance of 29% and a 25% reduction in system-level energy for a 0.5% loss in application-level quality.