Performance-asymmetry-aware topology virtualization for defect-tolerant NoC-based many-core processors

Topology virtualization techniques are proposed for NoC-based many-core processors with core-level redundancy to isolate hardware changes caused by on-chip defective cores. Prior work focuses on homogeneous cores with symmetric performance and optimizes on-chip communication only. However, core-to-core performance asymmetry due to manufacturing process variations poses new challenges for constructing virtual topologies. Lower performance cores may scatter over a virtual topology, while operating systems typically allocate tasks to continuous cores. As a result, parallel applications are probably assigned to a region containing many slower cores that become bottlenecks. To tackle the above problem, in this paper we present a novel performance-asymmetry-aware reconfiguration algorithm Bubble-Up based on a new metric called core fragmentation factor (CFF). Bubble-Up can arrange cores with similar performance closer, yet maintaining reasonable hop distances between virtual neighbors, thus accelerating applications with higher degree of parallelism, without changing existing allocation strategies for OS. Experimental results show its effectiveness.