Performance Interfaces for Hardware Accelerators

Designing and building a system that reaps the performance benefits of hardware accelerators is challenging, because they provide little concrete visibility into their expected performance. Developers must invest many person-months into benchmarking, to determine if their system would indeed benefit from using a particular accelerator. This must be done carefully, because accelerators can actually hurt performance for some classes of inputs, even if they help for others.

We demonstrate that it is possible for hardware accelerators to ship with performance interfaces that provide actionable visibility into their performance, just like semantic interfaces do for functionality. We propose an intermediate representation (IR) for accelerator performance that precisely captures all performance-relevant details of the accelerator while abstracting away all other information, including functionality. We develop a toolchain (ltc) that, based on the proposed IR, automatically produces human-readable performance interfaces that help developers make informed design decisions. ltc can also automatically produce formal proofs of performance properties of the accelerator, and can act as a fast performance simulator for concrete workloads.

We evaluate our approach on accelerators used for deep learning, serialization of RPC messages, JPEG image decoding, genome sequence alignment, and on an RMT pipeline used in programmable network switches. We demonstrate that the performance IR provides an accurate and complete representation of performance behavior, and we describe a variety of use cases for ltc and the resulting performance interfaces. ltc is open-source and freely available at https:// dslab.epfl.ch/research/perf.