Rescue: A Microarchitecture for Testability and Defect Tolerance

TLDR: This paper is the first to consider testability and fault isolation in designing modern high-performance, defect-tolerant microarchitectures, and defines intra-cycle logic independence (ICI) as the condition needed for conventional scan test to isolate faults quickly to themicroarchitectural-block granularity.

Abstract: Scaling feature size improves processor performance but increases each deviceýs susceptibility to defects (i.e., hard errors). As a result, fabrication technology must improve significantly to maintain yields. Redundancy techniques in memory have been successful at improving yield in the presence of defects. Apart from core sparing which disables faulty cores in a chip multiprocessor, little has been done to target the core logic. While previous work has proposed that either inherent or added redundancy in the core logic can be used to tolerate defects, the key issues of realistic testing and fault isolation have been ignored. This paper is the first to consider testability and fault isolation in designing modern high-performance, defect-tolerant microarchitectures. We define intra-cycle logic independence (ICI) as the condition needed for conventional scan test to isolate faults quickly to the microarchitectural-block granularity. We propose logic transformations to redesign conventional superscalar microarchitecture to comply with ICI. We call our novel, testable, and defect-tolerant microarchitecture Rescue. We build a verilog model of Rescue and verify that faults can be isolated to the required precision using only conventional scan test. Using performace simulations, we show that ICI transformations reduce IPC only by 4% on average for SPEC2000 programs. Taking yield improvement into account, Rescue improves average yield-adjusted instruction throughput over core sparing by 12% and 22% at 32nm and 18nm technology nodes, respectively.