Eliminating voltage emergencies via microarchitectural voltage control feedback and dynamic optimization

Abstract

Microprocessor designers use techniques such as clock gating to reduce power dissipation. An unfortunate side-effect of these techniques is the processor current fluctuations that stress the power-delivery network. Recent research has focused on hardware-only mechanisms to detect and eliminate these fluctuations. While the solutions have been effective at avoiding operating-range violations, they have done so at a performance penalty to the executing program. Compilers are well equipped to rearrange instructions such that current fluctuations are less dramatic, with minimal performance implications. Furthermore, a dynamic optimizer can eliminate the problem at run time, avoiding the difficult task of statically predicting voltage emergencies. This paper proposes complementing existing hardware solutions with additional run-time software to address problematic code sequences that cause recurring voltage swings. Our proposal extends existing hardware techniques to additionally provide feedback to a dynamic optimizer, which can provide a long-term solution, often without impacting the performance of the executing application. We found that recurring voltage fluctuations do exist in the SPEC2000 benchmarks, and that given very little information from the hardware, a dynamic optimizer can locate and correct many of the recurring voltage emergencies.