Vespa: Variability Emulation For System-On-Chip Performance Analysis

We address the problem of analyzing the performance of System-on-chip (SoC) architectures in the presence of variations. Existing techniques such as gate-level statistical timing analysis compute the distributions of clock frequencies of SoC components. However, we demonstrate that translating component-level characteristics into a system-level performance distribution is a complex and challenging problem due to the inter-dependencies between components' execution, indirect effects of shared resources, and interactions between multiple system-level "execution paths". We argue that accurate variation-aware system-level performance analysis requires repeated system execution, which is prohibitively slow when based on simulation. Emulation is a widely-used approach to drastically speedup system-level simulation, but it has not been hitherto applied to variation analysis. We describe a framework - Variability Emulation for SoC Performance Analysis (VESPA) - that adapts and applies emulation to the problem of variation aware SoC performance analysis. The proposed framework consists of three phases: component variability characterization, variation-aware emulation setup, and Monte-carlo driven emulation. We demonstrate the utility of the proposed framework by applying it to design variation-aware architectures for two example SoCs - an 802.11 MAC processor and an MPEG encoder. Our results suggest that variability emulation has great potential to enable variation-aware design and exploration at the system level.