why does speeding up the processor lead to missed deadlines in real time systems?

Question

A little confused about this. If I speed up the processor, wouldn't it take less time to do a task and therefore lead to making the deadline sooner?

thanks

Answer 1

The answer is that there may be new resource conflicts due to the faster speed. This is known as Graham’s anomaly: If a task set is scheduled on a multiprocessor such that schedule length is minimized, then increasing processors, reducing execution times, or weakening precedence constraints can increase schedule length. Note the objective (minimize schedule length). But the anomaly can easily be shown to be true if tasks have deadlines and the objective is to meet all task deadlines. This is well-documented with illustrations of examples in a number of books on operating systems.

See also:

• Andersson, B.; Jonsson, J.; , "Preemptive multiprocessor scheduling anomalies," Parallel and Distributed Processing Symposium., Proceedings International, IPDPS 2002, Abstracts and CD-ROM , vol., no., pp.12-19, 2002. doi: 10.1109/IPDPS.2002.1015483
• Grahamm R. L., "Bounds on Multiprocessing Timing Anomalies", SIAM Journal on Applied Mathematics , Vol. 17, No. 2 (Mar., 1969), pp. 416-429.