In context switching, generally, “context” means situation and “switching” means jumping from one option to another option. Hence, when the process keeps jumping or switching between the processor is referred to as context switching. Context switching is the changing in the state of processes so that a single CPU can be used by multiple processes.
A state renews several processes, this work is known as the context. Switching the processor by processes needs to function a state similar of the current process. Context switching is a property of a multitasking OS, and it permits an individual CPU to be common in several processes. We can’t directly switch a process from one state to another state, and it requires some steps to be followed.
What is Context Switching?
Context switching occurs when the operating system changes the CPU’s focus from one process or thread to another. This switch involves saving the state (or context) of the currently running process or thread so it can be resumed later and then loading the saved state of the next process or thread to be executed.
Components of a Process
The context of a process or thread includes its:
- Program Counter (PC): The address of the next instruction to execute.
- CPU Registers: The current working variables of the process.
- Stack Pointer: The pointer to the process’s stack in memory, containing temporary data such as function parameters, return addresses, and local variables.
- Process State: Information about the process’s current state, such as whether it is running, waiting, or stopped.
The steps included in the context switching are
- Initially, the context of the process (P1), which is present in the running state, will be kept in the PCB1 i.e., the process control block.
- After this, we have to change the PCB1 to the relevant queue like the waiting queue, ready queue and I/O queue.
- Now, choose the new process P2 from the ready queue that is to be run or executed.
- Renew the PCB2 by putting the process state to executing. Update the data structure with new process details.
- In the same way, when we want to run the process P1 once more, then we have to attend the above steps.
Costs and Implications
- Overhead: Context switching is not free; it incurs a performance cost due to the time taken to save and load contexts, as well as the potential for cache and memory access inefficiencies.
- Responsiveness: Despite its costs, context switching is essential for maintaining system responsiveness, allowing the operating system to quickly switch between tasks to handle user interactions and system events efficiently.
- Scheduling: The efficiency of context switching depends on the operating system’s scheduling algorithm, which determines the order and timing of task execution to optimize performance and responsiveness.
Optimizations
To minimize the costs associated with context switching, operating systems employ various strategies, such as:
- Thread Prioritization: Prioritizing threads to reduce the frequency of switches between low-priority tasks.
- Affinity Scheduling: Attempting to keep processes on the same CPU to take advantage of cache locality.
- Reducing Overhead: Streamlining the context switch process and optimizing data structures to speed up the save/load operations.
Advantages and Disadvantages Context Switching
Advantages
Context Switching helps to achieve multitasking. Multitasking provides us with an imagination that the processor executes multiple processes simultaneously.
In actuality, a single task is being executed at an instant of time by a CPU. But here, switching is so rapid, due to this, we feel that the CPU is executing multiple processes at one time.
Disadvantages
It needs some context switching time to save the context. During this time, the processor can’t do any useful work from the client’s viewpoint.