Aggressive Slack Recycling via Transparent Pipelines

Abstract

In order to operate reliably and produce expected outputs, modern architectures set timing margins conservatively at design time to support extreme variations in workload and environment. Unfortunately, the conservative guard bands set to achieve this reliability create clock cycle slack and are detrimental to performance and energy efficiency. To combat this, we propose Aggressive Slack Recycling via Transparent Pipelines. Our proposal performs timing speculation while allowing data to flow asynchronously via transparent latches, between synchronous boundaries. This allows timing speculation to cater to the average slack across asynchronous operations rather than the slack of the most critical operation - maximizing slack conservation and timing speculation efficiency. We design a slack tracking mechanism which runs in parallel with the transparent data path to estimate the accumulated slack across operation sequences. The mechanism then appropriately clocks synchronous boundaries early to minimize wasted slack and maximize clock cycle savings. We implement our proposal on a spatial fabric and achieves absolute speedups up to 20% and relative improvements (vs. competing mechanisms) of up to 75%.