Worst-case execution time

The worst-case execution time (WCET) of a computational task is the maximum length of time the task could take to execute on a specific hardware platform. The worst-case execution time (WCET) of a computational task is the maximum length of time the task could take to execute on a specific hardware platform. Worst case execution time is typically used in reliable real-time systems, where understanding the worst case timing behaviour of software is important for reliability or correct functional behaviour. As an example, a computer system that controls the behaviour of an engine in a vehicle might need to respond to inputs within a specific amount of time. One component that makes up the response time is the time spent executing the software – hence if the software worst case execution time can be determined, then the designer of the system can use this with other techniques such as schedulability analysis to ensure that the system responds fast enough. While WCET is potentially applicable to many real-time systems, in practice an assurance of WCET is mainly used by real-time systems that are related to high reliability or safety. For example, in airborne software some attention to software is required by DO178B section 6.3.4. The increasing use of software in automotive systems is also driving the need to use WCET analysis of software. In the design of some systems, WCET is often used as an input to schedulability analysis, although a much more common use of WCET in critical systems is to ensure that the pre-allocated timing budgets in a partition-scheduled system such as ARINC 653 are not violated.