RTOS terminology

Before dive in the exciting world of real-time operating systems, we need to understand the basic terminology.

What is latency?
The time elasped between a demand issued on a computer system and the begining of a response to the same demand is called latency or response time.

Kinds of latencies:

Interrupt Latency:
The time elapsed between the generation of an interrupt and the start of the execution of the corresponding interrupt handler. Example: When a hardware device performs a task, it generates an interrupt. This interrupt has the information about the task to be performed and about the interrupt handler to be executed. The interrupt handler then performs the particular task.

Scheduling Latency:
It is the time between a wakeup signaling that an event has occurred and the kernel scheduler getting an opportunity to schedule the thread that is waiting for the wakeup to occur (the response). Scheduling latency is also known as dispatch latency.

Worst-case Latency:
The maximum amount of time that can laspe between a demand issued on a computer system and the begining of a response to the same demand.

What is throughput?
Amount of work that a computer can do in a given period of time is called throughput.

What is Context switch?
Context switch is the switching of the CPU from one process/thread to another. Context switches can occur only in kernel mode. This is the process of saving the current execution state of the process (for resuming execution later on), and loading the saved state of the new process/thread for execution.


(source: https://stackoverflow.com/questions/10042550/disadvantages-of-preempt-rt)

(image from: http://free­electrons.com)

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