Question 2 Describe the actions taken by the kernel to context-switch between two processes. Visit our YouTube channel for more content. In this phenomenon, the execution of the process that is present in the running state is suspended by the kernel and another process that is present in the ready state is executed by the CPU. 3. You have to save the context of that process. Interrupt causes the operating system to change a CPU from its current task and to run a kernel routine. Any operating system that allows for multitasking relies heavily on the use of context switching to allow different processes to run at the same time . Context Switch in Operating System Processes, Any operating system that allows for multitasking relies heavily on the use of context switching to. Save the context of the process that is currently running on the CPU. When a process of high priority comes in the ready state. So, the context of the process should be saved before putting any other process in the running state. Select a new process for execution. But in reality, only one task is being executed at a particular instant of time by a processor. In the Operating System, there are cases when you have to bring back the process that is in the running state to some other state like ready state or wait/block state. It is one of the essential features of the multitasking operating system. PCB1. 2. The disadvantage of context switching is that it requires some time for context switching i.e. This includes updating the process state to running. The kernel must save the context of the previous process in its Process Control Block and then must load the saved context of the new process which is scheduled to run. A context switch is the mechanism to store and restore the state or context of a CPU in Process Control block so that a process execution can be resumed from the same point at a later time. So, let's get started. Move the process control block of the above process into the relevant queue such as the ready queue, I/O queue etc. So, context switching is pure overhead in this condition. on behalf of the operating system, it’s not safe for user programs to be able to service or ignore interrupts, nor is it safe for them to have raw access to devices. The processes are switched so fastly that it gives an illusion to the user that all the processes are being executed at the same time. From the ready state, select the new process that is to be executed i.e. In the above figure, you can see that initially, the process P1 is in the running state and the process P2 is in the ready state. Similarly, if you want to execute the process P1 again, then you have to follow the same steps as mentioned above(from step 1 to 4). Context switching can happen due to the following reasons: The process of context switching involves a number of steps. Sometimes, the process might be using a round-robin scheduling algorithm where after every fixed time quantum, the process has to come back to the ready state from the running state. Describe the actions taken by a kernel to context-switch between processes. Answer: 1. A typical process context switch happens like this: Process context switches are initiated by a thread-context switch, so all of the above, 1-9, is going to need to happen. Typically, there are three situations that a context switch is necessary, as shown below. In this case, the execution of the running process should be stopped and the higher priority process should be given the CPU for execution. the process P2. This may be required, depending on how address translation is managed. PCB2 by setting the process state to running. You can't directly switch a process from the running state to the ready state. In response to a clock interrupt, the OS saves the PC and user stack pointer Do share this blog with your friends to spread the knowledge. If the running process wants to perform some I/O operation, then you have to remove the process from the running state and then put the process in the I/O queue. ... Action taken by kernel to context switch between processes. The time involved in the context switching of one process by other is called the Context Switching Time. This includes changing the state of this process to Running. In this blog, we will learn about the concept of Context Switching in the Operating System and we will also learn about the advantages and disadvantages of Context Switching. A context switch occurs when a computer’s CPU switches from one process or thread to a different process or thread. The time involved in the context switching of one process by other is called the Context Switching Time. Now, you have to move the PCB1 to the relevant queue i.e. That's it for this blog. The steps involved in context switching are as follows: 1. Update the process control block of the process selected. Update the process control block of the selected process. If the process P2 was earlier executed by the CPU, then you can get the position of last executed instruction so that you can resume the execution of P2. At step 5 above, the scheduler decides to run a thread belonging to a different process from the one that owned the previously-running thread. But in reality, it should continue from that point where it left the CPU in its previous execution. multiprogramming with time-sharing(learn more about multitasking from here). the process present in the running state will be saved in the Process Control Block of process P1 i.e. Whenever an interrupt arrives, the CPU must do a state-save of the currently running process, then switch into kernel mode to handle the interrupt, and then do a state-restore of the interrupted process. If you are not saving the context of any process P then after some time, when the process P comes in the CPU for execution again, then the process will start executing from starting. But the context switching process involved a number of steps that need to be followed. When an interruption occurs then the process in the running state should be stopped and the CPU should handle the interrupt before doing something else. So, these process switchings are done with the help of Context Switching. the context switching time. Now, update the Process Control Block of process P2 i.e. Here, the context switching is so fast that the user feels that the CPU is executing more than one task at the same time. A context is the contents of a CPU's registers and program counter at any point in time. Switching the CPU to another process required performing a state save of the current process and state restore of different process and this task is known as context switching. ready queue, I/O queue, waiting queue, etc. Context switching is used to achieve multitasking i.e. Time is required to save the context of one process that is in the running state and then getting the context of another process that is about to come in the running state. Multitasking gives an illusion to the users that more than one process are being executed at the same time.