CSE 291-a Interconnection Networks

CSE 291-aInterconnection Networks Lecture 12: Deadlock Avoidance (Cont’d)Router February 28, 2007 Prof. Chung-Kuan Cheng CSE Dept, UC San Diego Winter 2007 Transcribed by Yi Zhu

Topics • Deadlock avoidance • Restricted physical route (lecture 10) • Resource classes • Distance classes • Dateline (ring) • Duato’s protocol • Router Architecture

Distance Classes • #classes >= diameter of network • At source, we inject packets into resource of class 0 • At each hop, the packet of class i acquires a resource of class i+1 • Use min routing

Dateline (Ring) • There are two classes • A dateline cuts the ring into a string • At source, we inject packets into resources of class 0 • Packets remain in the same class, but jump to class 1 when crossing the dateline

Dateline (Ring)

Duato’s Protocol for Deadlock-Free Adaptive Algorithm • The underlying network is deadlock-free. The routing relation is R1: escape routing • Create new virtual resources and routing relation Rc • Rc -> R1 works as injection at the node. • R1 -> Rc not allowed

Router Architecture state Physical channel Physical channel buffer

Virtual Channel State • Virtual channel state fields: 5-vector GROPC • G: Global state • I (idle), • R (routing) • V (waiting for VC) • A (active) • C (waiting for credits) • R: Route, output port R for the packet • O: Output VC, output VC O of port R

Virtual Channel State (Cont’d) • P: Pointers, flit head and flit tail pointers into the input buffer • C: Credit count, #credits C for VC O of port R

CSE 291-a Interconnection Networks