DeCoR: a delayed commit and rollback mechanism for handling inductive noise

Increases in peak current draw and reductions in the operating volt-ages of processors continue to amplify the importance of dealing with voltage fluctuations in processors. Noise-margin violations lead to undesired effects, like timing violations, which may re-sult in incorrect execution of applications. To support future trends, several recent architectural solutions for inductive noise have been proposed that, unfortunately, have a strong correlation to the un-derlying power-delivery package model and require a feedback loop that is largely constrained by the voltage/current sensor speed and accuracy. The resulting solutions are not robust across a range of microprocessor designs and packaging technologies. This pa-per proposes a robust scheme that does not make any assump-tions about the package model or the responsiveness of the voltage sensors. In particular, our approach recovers from, rather than at-tempting to avoid, voltage emergencies. It uses a Delayed-Commit and Rollback scheme (DeCoR), which guarantees correct recov-ery even when noise margins are exceeded. The approach incurs a small performance impact when compared to an ideal machine that does not have voltage emergencies. We show that explicit checkpoint-recovery schemes, intended to handle infrequent events (e.g., radiation-induced soft errors), fail to handle frequently oc-curring voltage emergencies due to prohibitively high performance costs. DeCoR requires very few modifications to modern processor designs, as it simply leverages the existing buffering of the proces-sor store queue and reorder buffer. Unlike conventional designs that conservatively protect all components of the processor from induc-tive noise with large timing margins, our approach conservatively protects only the architected register state and cache write paths. 1