Pull-off buffer: Borrowing cache space to avoid deadlock for fault-tolerant NoC routing

Advances in semiconductor technology have led to large chip multiprocessor (CMP) employing network-on-chip (NoC) to provide scalable on-chip communication. This higher integration capacity, on the other hand, increases the possibility of faults. To tackle this challenge, fault-tolerant routing in NoC becomes essential, which allows packets to be routed around faulty network components and maintains normal communication. However, to tolerate a large number of faults, the deadlock problem becomes very difficult to deal with. Existing highly fault-tolerant routing solutions employ virtual channel (VC) or topology-agnostic routing for deadlock avoidance, but at the cost of lower network performance and the demand for extra hardware. In this paper, we show that it is possible to design a novel highly fault-tolerant routing method without VC and topology-agnostic routing. We present pull-off buffer (POB), a FIFO buffer borrowing the space already present in cache, to avoid potentially existing deadlocks. POBs borrow cache space only from selected nodes and only after the occurrence of faults. The space of caches at other nodes will not be affected. Experimental results show that our solution can provide 2x to 3x higher network throughput and reduce router area and power overhead, when compared against existing highly fault-tolerant routing methods employing VC or topology-agnostic routing.