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Journal of Computer Systems, Networks, and Communications
Volume 2008 (2008), Article ID 583162, 7 pages
http://dx.doi.org/10.1155/2008/583162
Research Article

Internal Clock Drift Estimation in Computer Clusters

Department of Computer and Software Engineering, Ecole Polytechnique, P.O. Box 6079, Downtown, Montreal, QC, Canada H3C 3A7

Received 22 August 2007; Revised 12 February 2008; Accepted 4 May 2008

Academic Editor: Wael Badawy

Copyright © 2008 Hicham Marouani and Michel R. Dagenais. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Most computers have several high-resolution timing sources, from the programmable interrupt timer to the cycle counter. Yet, even at a precision of one cycle in ten millions, clocks may drift significantly in a single second at a clock frequency of several GHz. When tracing the low-level system events in computer clusters, such as packet sending or reception, each computer system records its own events using an internal clock. In order to properly understand the global system behavior and performance, as reported by the events recorded on each computer, it is important to estimate precisely the clock differences and drift between the different computers in the system. This article studies the clock precision and stability of several computer systems, with different architectures. It also studies the typical network delay characteristics, since time synchronization algorithms rely on the exchange of network packets and are dependent on the symmetry of the delays. A very precise clock, based on the atomic time provided by the GPS satellite network, was used as a reference to measure clock drifts and network delays. The results obtained are of immediate use to all applications which depend on computer clocks or network time synchronization accuracy.