Low-cost per-core voltage domain support for power-constrained high-performance processors

Per-core voltage domains can improve performance under a power constraint. Most commercial processors, however, only have a single voltage domain for all processor cores. This is because splitting the single voltage domain into per-core voltage domains and powering them with multiple off-chip voltage regulators (VRs) incur a high cost for the platform and package designs. Although using on-chip switching VRs can be an alternative solution, integrating high-quality inductors for VRs with cores has been a technical challenge. In this paper, we propose a cost-effective power delivery technique to support per-core voltage domains. Our technique is based on the observations that: 1) core-to-core (C2C) voltage variations are relatively small for most execution intervals when the voltages/frequencies are optimized to maximize performance under a power constraint and 2) per-core power-gating devices augmented with feedback control circuitry can serve as low-cost VRs that can provide high efficiency in situations like 1). Our experimental results show that processors using our technique can achieve power efficiency as high as those using the per-core on-chip switching VRs at a much lower cost.