Reference: https://www.rapitasystems.com/blog/difference_between_execution_times_and_response_times
task: a piece of code that is to be run within a single thread of execution. A task issues a sequence of jobs to the processor which are queued and executed.
execution time: the time spent by the job actively using processor resources. The execution time of each job instance from the same task is likely to differ, due to path data dependencies (the path taken through the code depends on input parameters) and hard-to-predict hardware features such as branch prediction, instruction pipelining and caches.
response time: the time between when it becomes active (e.g. an external event or timer triggers an interrupt) and the time it completes.
priority inversion: A lower priority job can also prevent a job from running if it locks a shared resource before the higher priority job does.
High level system requirements will specify maximum response times for a task, known as a deadline. WCRTs are calculated using response time analysis which takes WCETs and a scheduling policy as inputs. This may lead to execution time budgets and a scheduling policy being derived as lower level requirements. This is usually in the context of worst-case execution times(WCETs) and worst-case response times (WCRTs).
