This is a common misconception about RTOSes, or at least needs to be further qualified with soft real time vs hard real time OSes. RTOSes provide schedulers and multitasking mechanisms for context switching between tasks. Tasks can be assigned priorities. A higher priority task can pre-empt a lower priority task (depending on the RTOS’ scheduler implementation). In that case, you may never get your cycles, or at least not deterministically. tl;dr, depends on the scheduler implementation.