Pipeline muffling and a priori current ramping: architectural techniques to reduce high-frequency inductive noise

While circuit and package designers have addressed microprocessor inductive noise issues in the past, multi-gigahertz clock frequencies and billion-transistor-level integration are exacerbating the problem, necessitating microarchitectural solutions. The large net on-die decoupling capacitance used to address this noise throughout the chip consumes substantial area and can cause a large leakage current. This paper proposes microarchitectural techniques to reduce high-frequency current variability, reducing the need for decoupling capacitors. We observe that we can control inductive noise by reducing current variability either in space (i.e., variability in usage of circuit blocks) or in time (i.e., variability within a circuit block across clock cycles). We propose pipeline muffling, a novel technique to reduce changes in the number of resources being utilized by controlling instruction issue, trading off some energy and performance to control di/dt in space. We also extend a previous technique, which incurs performance and energy degradation, and propose a priori current ramping to allow the current of a resource to ramp up ahead of usage, with virtually no performance loss, and ramp down immediately after usage, with little energy loss. Our techniques guarantee a worst-case bound on the di/dt, which is required to reduce the demand for decoupling capacitors, saving area and reducing leakage.