high performance router architectures for network-based computing
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High Performance Router Architectures for Network-based Computing
By Dr. Timothy Mark PinkstonUniversity of South California
Computer Engineering DivisionDept. of Electrical Engineering-
Systems
Outline Introduction Topology Routing Deadlock Network Reconfiguration
Introduction High-Performance Router Architectures
for Network-based Computing Multiprocessor system Cluster computing environment Core components within the switch/router
Network Latency as a function of time for transmission of packet propagation delay switching delay Time required for contention handling
Introduction Four major areas of concern of network
design Topology
Defines the network architecture Routing
Path selection, deadlock handling, congestion & load balancing
Switching Path set-up, degree of pipelining, channel sharing
Flow control Resource allocation, contention resolution,
channel sharing,scheduling
Topology Bisection width
Number of links that needed to be removed when dividing the network into 2 nearly equal half
Larger width Latency is lower May not be scalable
Routing-Oblivious vs. Adaptive
Oblivious routing Path selection in regardless of load Pro: Simple routing function result in
lower switching delay Con: Unable to adapt to network
condition result in higher contention delay
Routing Oblivious vs. Adaptive Adaptive routing
Path selection based on network status
Pro: Distribute load more evenly result in lower contention delay
Con: Decision based on local information can
cause congestion More complex decision logic can increase
the switching delay
Routing – Minimal vs. Non-minimal Minimal routing
Packets consume less bandwidth Minimal path may consists
congested/faulty node Non-minimal routing
Packets can route around congestion Provide better worst case
performance
Routing - Deadlock Cause
Congestion lead to cyclic waits for resources Theorem
If no cycles appear in directed graph or connected sub-graph, then it is deadlock-free
Solutions Avoidance based Recovery based
Deadlock – Avoidance based
Path-based Observation
Deadlocks occur when packet change their direction in the network
Idea Prohibit certain turns so as to eliminate
cycles Examples
Direction Order Routing Turn Model Up/Down Model
Path-based Example Dimension Order Routing
Turn Model
Deadlock – Avoidance based Path-based
Pro: Does not depend on virtual circuits for
deadlock-freedom Con:
Routing flexibility is sacrificed in general case
Deadlock – Avoidance based Channel based
Observation Deadlocks occur when packet cannot escape from
cyclic resource dependency Idea
Explicitly impose an ordering on the use of virtual circuit resources
Examples Entire channel set Escape channel set
Deadlock – Avoidance based Channel based
Pro: No need for replication of physical
channels Con:
Additional control needed for channel selection
Network Reconfiguration Why?
To restore or make more efficient the network connectivity when nodes fail/are added
Goal Keep network up and running during
reconfiguration Discard as few packets as possible
How? Static Reconfiguration Dynamic Reconfiguration
Static Reconfiguration Three steps
Stop all network traffic and discard all existing packets
Update the routing function Reactivate the network
Problem Poor reliability, availability,
performance and predictability
Dynamic Reconfiguration Problem
Reconfiguration-dependent deadlocks due to ghost dependencies: interaction of old and new routing functions
Duato’s Theory Only need to ensure that the escape path
(particular VC) remains cycle-free during reconfiguration
Dynamic Reconfiguration Application of Duato’s theory
Escape channel resources doubled during reconfiguration
One of the normal channels is drained and configures as the new escape resource
Reconfiguration done with 2 escape channels Old escape resource is used as a new adaptiv
e resource
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