Using hardware vulnerability factors to enhance AVF analysis

Fault tolerance is now a primary design constraint for all major microprocessors. One step in determining a processor's compliance to its failure rate target is measuring the Architectural Vulnerability Factor (AVF) of each on-chip structure. The AVF of a hardware structure is the probability that a fault in the structure will affect the output of a program. While AVF generates meaningful insight into system behavior, it cannot quantify the vulnerability of an individual system component (hardware, user program, etc.), limiting the amount of insight that can be generated. To address this, prior work has introduced the Program Vulnerability Factor (PVF) to quantify the vulnerability of software. In this paper, we introduce and analyze the Hardware Vulnerability Factor (HVF) to quantify the vulnerability of hardware. HVF has three concrete benefits which we examine in this paper. First, HVF analysis can provide insight to hardware designers beyond that gained from AVF analysis alone. Second, separating AVF analysis into HVF and PVF steps can accelerate the AVF measurement process. Finally, HVF measurement enables runtime AVF estimation that combines compile-time PVF estimates with runtime HVF measurements. A key benefit of this technique is that it allows software developers to influence the runtime AVF estimates. We demonstrate that this technique can estimate AVF at runtime with an average absolute error of less than 3%.