Title:  Subactive Techniques For Guaranteeing Routing And Protocol Deadlock Freedom In Interconnection Networks

Committee:

Dr. Tushar Krishna, ECE, Chair , Advisor

Dr. Hyesoon Kim, ECE

Dr. Alexandros Daglis, ECE

Dr. Moinuddin Qureshi, ECE

Dr. Paul Gratz, Texas A&M

Abstract: Interconnection networks are the communication backbone for any system. They occur at various scales: from on-chip networks between processing cores, to supercomputers between compute nodes, to data centers between high-end servers. One of the most fundamental challenges in an interconnection network is that of deadlocks. Deadlocks can be of two types: routing level deadlocks and protocol level deadlocks.  Routing level deadlocks occur because of cyclic dependency between packets trying to acquire buffers, whereas protocol level deadlock occurs because the response message is stuck indefinitely behind the queue of request messages. Both kinds of deadlock render the forward movement of packets impossible leading to complete system failure. Prior work either restricts the path that packets take in the network or provisions an extra set of buffers to resolve routing level deadlocks. For protocol level deadlocks, separate sets of buffers are reserved at every router for each message class. Naturally, proposed solutions either restrict the packet movement resulting in lower performance or require higher area and power. In this thesis, we propose a new set of efficient techniques for providing both routing and protocol level deadlock freedom. Our techniques provide periodic forced movement to the packets in the network, which breaks any cyclic dependency of packets. Breaking this cyclic dependency results in resolving routing level deadlocks. Moreover, because of periodic forced movement, the response message is never stuck indefinitely behind the queue of request messages; therefore, our techniques also resolve protocol level deadlocks. We use the term `subactive' for these new class of techniques.