Wormhole Switching Intermediate nodes Destination node ource node Large packets are divided into small flits a An entire packet need not be buffered to move on to the next node increas i throughput o More efficient use of buffers than virtual cut-through o Bandwidth and channel allocation gre couple
22 Source node Intermediate nodes Destination node ❑ Large packets are divided into small flits ❑ An entire packet need not be buffered to move on to the next node, increasing throughput. ❑ More efficient use of buffers than virtual cut-through ❑ Bandwidth and Channel allocation are decoupled Wormhole Switching
Wormhole Switching Intermediate nodes Destination node ource node Large packets are divided into small flits a An entire packet need not be buffered to move on to the next node increas i throughput o More efficient use of buffers than virtual cut-through o Bandwidth and channel allocation gre couple
23 Source node Intermediate nodes Destination node ❑ Large packets are divided into small flits ❑ An entire packet need not be buffered to move on to the next node, increasing throughput. ❑ More efficient use of buffers than virtual cut-through ❑ Bandwidth and Channel allocation are decoupled Wormhole Switching
Wormhole Switching Intermediate nodes Destination node ource node Large packets are divided into small flits a An entire packet need not be buffered to move on to the next node increas i throughput o More efficient use of buffers than virtual cut-through o Bandwidth and channel allocation gre couple
24 Source node Intermediate nodes Destination node ❑ Large packets are divided into small flits ❑ An entire packet need not be buffered to move on to the next node, increasing throughput. ❑ More efficient use of buffers than virtual cut-through ❑ Bandwidth and Channel allocation are decoupled Wormhole Switching
Wormhole Switching Header flit 「∴ Link ,… Single Flit wormhole Time Busy Message are pipelined, but buffer space is on the order of a few flits Small buffers+message pipelining >small compact switches/routers a Messages cannot be interleaved over a channel routing information is only associated with the leader
❑ Message are pipelined, but buffer space is on the order of a few flits ❑ Small buffers + message pipelining → small compact switches/routers ❑ Messages cannot be interleaved over a channel: routing information is only associated with the header Link Time Busy tr ts twormhole Single Flit Header Flit 25 Wormhole Switching
Wormhole Example Red holds this channel Channel idle but channel remains idle red packet blocked until read proceeds behind blue Buffer full: blue cannot procee Blocked by other 6 flit buffers/input port 26
Wormhole Example ❑ 6 flit buffers/input port Blocked by other packets Channel idle but red packet blocked behind blue Buffer full: blue cannot proceed Red holds this channel: channel remains idle until read proceeds 26