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Vishal Sharda Ashima Gupta. Comparing Topology based Collective Communication Algorithms. Work progress. No up-to-date open source solution available for fully mapping the network to build upon Nomad, Cheops, Nagios, ENV, Argus etc. outdated - PowerPoint PPT Presentation
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Comparing Topology based Collective Communication
Algorithms
• Vishal Sharda• Ashima Gupta
Work progress
• No up-to-date open source solution available for fully mapping the network to build upon
• Nomad, Cheops, Nagios, ENV, Argus etc. outdated
• Use of a third-party service to determine the topology
• Java applet to map SERC network
Status of current study
• Nearly all the research on this problem till now considers tightly-coupled systems.
• Thus, most of the algorithms assume point-to-point connectivity.
• So, these have to be modified to adapt to the network of heterogeneous workstations.
All to all broadcast
• Also known as multinode broadcast
• Generalization of one-to-all broadcast in which all the processors simultaneously initiate a broadcast.
• Different processors may send out different message.
Existing Algorithms
• Direct exchange
• Circular all-to-all
• E1 algorithm
• Liquid Schedule
• Algorithms for specific topologies like start and mesh.
Direct Exchange
• Simplest approach
• Assumes point to point connectivity
• Each node simultaneously sends data to each other node
• Involves lot of congestion
Circular all-to-all
• Let p be the no. of nodes
• For each node i for step k in {1..p}, node i
sends to (i+k)mod p
receives from(i-k+P)mod p
E1 algorithm
• One node receives messages from all other nodes(becomes an expert)
• Experts are formed by recursively doubling existing experts.
Liquid schedule algorithm
• Traffic is the set of all collective exchanges.
• A simultaneous sub traffic is part of the traffic involing non-congesting transfers.
• Identify the bottleneck links in the network.
• A liquid schedule is such that all the bottleneck links are utilized in every sub-traffic.
Need for Simulation
• Deciding the packet to follow a particular route needs to bypass router decisions– Needs DLL operations.
• Focus on comparing the algorithms– Incorporate simulation-based study like
standard experiments.
Basis of Simulation
• Execute and compare the algorithms for the network specifed at the interface.
• Some algorithms will take bandwidth of the links into account.
• Depending on the input, an algorithm may or may not show good results.
Implementation Approach
• Network represented as weighted undirected graph with weights inversely proportional to bandwidth.
• Simulating n processes on different nodes in a network with Java threads.
• First of all, each node will compute the shortest path to all other nodes using single source shortest path algorithm.
Handling Collision
• Lot of collision involved in all-to-all broadcast.
• Several approaches possible like partitioning into subnets , choosing alternate link.
• Our approach will be to stick to the shortest link and if collision detected then wait for random time and sense again.
ReferencesPapers :
• "ECO: Efficient Collective Operations for Communication on Heterogeneous Networks",Bruce B. Lowekamp and Adam Begueliny.
• "Network Topology Aware Scheduling of Collective Communications",Emin Gabrielyan, Roger D. Hersch.
• "On General Results for all-to-all broadcast", Ming-Syan Chen et. al
• “Efficient all-to-all broadcast in star graph interconnecion networks",Yu-Chee Tseng et.al
Websites:• freemap.qualys.com