An optimal scheduling algorithm for an agent-based multicast strategy on irregular networks

Abstract

This paper describes an agent-based approach for scheduling multiple multicast on wormhole switch-based networks with irregular topologies. Multicast/broadcast is an important communication pattern, with applications in collective communication operations such as barrier synchronization and global combining. Our approach assigns an agent to each subtree of switches such that the agents can exchange information efficiently and independently. The entire multicast problem is then recursively solved with each agent sending message to those switches that it is responsible for. In this way, communication is localized by the assignment of agents to subtrees. This idea can be easily generalized to multiple multicast since the order of message passing among agents can be interleaved for different multicasts. The key to the performance of this agent-based approach is the message-passing scheduling between agents and the destination processors. We propose an optimal scheduling algorithm, called ForwardInSwitch to solve this problem. We conduct extensive experiments to demonstrate the efficiency of our approach by comparing our results with SPCCO, a highly efficient multicast algorithm reported in literature. We found that SPCCO suffers link contention when the number of simultaneous multiple multicast becomes large. On the other hand, our agent-based approach achieves better performance in large cases.

Scheduling contention‐free broadcasts in heterogeneous networks

“…The fastest workstation of each switch will be selected as the group head; they are 9, 7, 1, 22, 13, 4, 16, and 19. With checking the size of subtrees, the three groups, (4,5,6), (16,17,18), and (19,20,21) will be adjusted in order to obtain a better scheduling tree. The adjusted spanning tree is shown in Figure 13.…”

“…The VBBS algorithm [9] used the post-order doubling algorithm [4] containing up*/down* routing and the ordered chain property as the basic routing to avoid link contention. Liu et al proposed an agent-based multicast algorithm to avoid link contention by localizing and interleaving message passing in multicast [5].…”

“…Moreover, all workstations are sorted by ascending speed types in Figure 12. The post-order list of workstations (9,10,11,12,7,8,1,2,3,22,23,24,25,13,14,15,4,5,6,16,17,18,19,20,21) is obtained from the LST. The fastest workstation of each switch will be selected as the group head; they are 9, 7, 1, 22, 13, 4, 16, and 19.…”

“…However, as known in literature, it is an NP-complete problem [1,2] to determine an optimal scheduling tree. As a result, there are many research has been proposed in conducting various communication optimization techniques on Networks of Workstations (NOW) [3][4][5][6]. The NOW has properties such as high bandwidth, high scalability, high flexibility, and cost effective.…”

“…The communication model of peer-to-peer message passing; notations (1), (2), (4), and (5) correspond to equations (1), (2), (4), and(5).…”