Comparative Assessment and Evaluation of Jitter Control Methods

Most control systems involve the execution of periodic activities, which are automatically activated by the operating system at the specified rates. When the application consists of many concurrent tasks, each control activity may experience delay and jitter, which depend on several factors, including the scheduling algorithm running in the kernel, the overall workload, the task parameters, and the task interactions. If not properly taken into account, delays and jitter may degrade the performance of the system and even jeopardize its stability.
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In this paper, we evaluate three methodologies for reducing the jitter in control tasks: the first one consists of forcing the execution of inputs and outputs at the period boundaries, so trading jitter with delay; the second method reduces jitter and delay by assigning tasks shorter deadlines; whereas, the third method relies on non preemptive execution. We compare these techniques by illustrating examples, pointing out advantages and disadvantages, and evaluating their effects in control applications by simulation. It is found that the deadline advancement method gives the better control performance for most configurations.