Reunion: Complexity-Effective Multicore Redundancy

Wednesday December 6, 2006
Hamerschlag Hall D-210
4:30 pm

This is a practice talk for MICRO-39.

Jared Smolens
Carnegie Mellon University

To protect processor logic from soft errors, multicore redundant architectures execute two copies of a program on separate cores of a chip multiprocessor (CMP). Maintaining identical instruction streams is challenging because redundant cores operate independently, yet must still receive the same inputs (e.g., load values and shared-memory invalidations). Past proposals strictly replicate load values across two cores, requiring significant changes to the highly-optimized core.

We make the key observation that, in the common case, both cores load identical values without special hardware. When the cores do receive different load values (e.g., due to a data race), the same mechanisms employed for soft error detection and recovery can correct the difference. This observation permits designs that relax input replication, while still providing correct redundant execution. In this paper, we present Reunion, an execution model that provides relaxed input replication and preserves the existing memory interface, coherence protocols, and consistency models. We evaluate a CMP-based implementation of the Reunion execution model with full-system, cycle-accurate simulation. We show that the performance overhead of relaxed input replication is only 5% and 6% for commercial and scientific workloads, respectively.

Jared Smolens is a PhD candidate in the ECE department at Carnegie Mellon University, where he is advised by Prof. James Hoe. He received his BS and MS in ECE from Carnegie Mellon University. His research interests are in multiprocessor and microprocessor architectures, fault tolerance, and performance modeling.