Performance Analysis of Wormhole
Switching with adaptive Routing in a
Two-Dimensional Torus
M.Colajamin, B.Ciciani, and
F.Quaglia
Summary
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Introduction to Wormhole switching
Deadlocks in wormhole switching
Adaptive Routing
System Model
Analysis
Reference
Switching Techniques
Switching techniques
Packet Switching
Circuit Switching
Virtual Cut through
Wormhole Switching
Wormhole Switching
In worm hole switching a message is
transmitted as a continuous stream of
bits, physically occupying a sequence of
nodes/edges in the network. Thus a
message resembles worm borrowing
through the network.
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Packet is transmitted
from a node as flit(
smallest unit on
which flow control
can be performed).
Flits of two
messages cannot be
interleaved.
Transmission
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Two kinds of Flits Header flit and Data flit.
Header Flit tries to get the another channel
while the data flits are transmitted through
the already obtained channels.
In case of channel contention , the flits are
stored in the flit buffers of the nodes along
the already established path.
A channel is released only when the last flit of
the message is passed though it.
Advantages of wormhole
routing
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The transmission latency is insensitive of the distance
between the source and the destination.
Requires Less buffer space since the intermediate
nodes need to store on only one flit.
Used in distributed memory multiprocessors including
switches for networks of workstations.
using wormhole based switches can significantly
improve latency characteristics of clusters.
Wormhole switching with
Virtual Channels
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Virtual Channels are used in wormholes
switching for avoiding deadlock.
Virtual channels make it possible for
several independent messages to use
the same physical channel by providing
multiple buffers.
Virtual Channels …
Deadlocks in Wormhole
Switching
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Header Flit contains all the routing
information that is required to move
data flits across the network. If the
header flit cannot move any further
then there will a congestion which
causes a chained block in the network
which leads to Deadlocks.
Adaptive Routing
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In adaptive routing the intermediate nodes can take
the actual network conditions, such as presence of
failures or bottlenecks, into account and determine
accordingly which neighbor the message should be
sent to.
Minimal Adaptive Routing -the path selected by the
algorithm is the shortest path between the source
and destination. In other words this routing will take
a path which will cause the message to move a step
closer to destination.
Fully Adaptive – the messages are allowed to follow
any of the minimal or non-minimal path.
System Model
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Each Node consists of a processing element,
a Router node Ni,j with a router node per
each node.
The network is balanced and all the channels
are equally likely to be visited.
Average Message – A message which travels
on exactly K channels in each dimension(K is
the average message length)
Flow Streams
 Βx – messages that use only channels
in X dimension
 Βy – messages that use only channels
in Y dimension
 α – messages that can use adaptive
path selection along both dimension.
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Residual Transmission Time Txi,j – the time
that header flit takes to reach destination
node from the node Xi,j.
Link Utilization time in wormhole switching is
equal to the mean time to transmit the entire
message plus the waiting to obtain the
remaining links of the path.
Mean Latency time is the weighted sum of
the residual transmission values of βx,βy,α.
References
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Advanced Computer Architectures – A
design approach. D. Sima, T.Fountain,
P.Kacsuk.