TR-97-8.ps.Z

Y. Dong, X. Du, and X. Zhang 

``Characterizing and scheduling communication tasks of parallel and 
sequential jobs on networks of workstations",  

Computer Communications, Vol. 21, No. 5, 1998, pp. 470-484. 
 
Abstract
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This paper examines the effects of communication interactions of parallel 
jobs on a non-dedicated NOW. Three representative communication 
patterns of parallel jobs are considered. A quantitative model 
to characterize the interactions is proposed. Measurement results 
on a NOW support the analytical model, and indicate that the network 
interface in the TCP/IP protocol forms a communication bottleneck during 
interactions because a standard netwrok interface with single 
input/output queue is not able to distinguish communication requests 
from parallel and local jobs. Therefore, small but important communication 
messages of a parallel job, such as a barrier synchronization, could 
be easily blocked by a communication request of a local job, which 
could degrade the performance of the parallel job significantly. 
A double queue scheme in the network interface is proposed. Using 
available information from the protocol layer, the scheme is able to 
distinguish the two types of communication requests and give a higher 
priority to parallel jobs' communication requests. The simulation 
results show that the scheme could improve the performance of parallel 
jobs without significantly affecting the performance of local jobs.