SEEC: Stochastic Escape Express Channel

Authors: Mayank Parasar (Georgia Institute of Technology); Natalie Enright Jerger (University of Toronto); Paul Gratz (Texas A&M University); Joshua San Miguel (University of Wisconsin, Madison); and Tushar Krishna (Georgia Institute of Technology)

Abstract: Allocating a free buffer before moving to the next router is a fundamental tenet for packet movement in NoCs. There are two challenges, however. First, if there is a cyclic dependency among the buffers, it can lead to deadlock. Second, if buffers are full of packets going towards congested regions, other packets can get blocked. In this work, we introduce stochastic escape express channels (SEEC). The network interfaces in SEEC send special tokens called seekers to find packets destined for them and upgrade them to use a novel flow control called Free-Flow (FF). FF-packets traverse the network minimally from link to link, bypassing routers (bufferlessly) to the destination. Thus any deadlock in which an FF-packet was originally involved is guaranteed to break, without requiring turn restrictions or extra VCs. We also present an extension called multi-SEEC (mSEEC) that enables multiple simultaneous non-intersecting FF-packet traversals to further enhance throughput.




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