GO Classes Test Series 2024 | Mock GATE | Test 14 | Question: 23

Question

Consider the context switch of a CPU from the context of process P1 to that of process P2.

Consider the following two events in the chronological order of the events during the context switch:

• E1: The stack pointer shifts from pointing to the kernel stack of $\mathrm{P} 1$ to the kernel stack of $\mathrm{P} 2$;
• E2: The program counter shifts from pointing to an address in the memory allocated to $\mathrm{P} 1$ to an address in the memory allocated to P2.

Which of the following statements is/are true regarding the relative ordering of events E1 and E2?

• A. E1 occurs before E2.
• B. E2 occurs before E1.
• C. E1 and E2 occur simultaneously via an atomic hardware instruction.
• D. The relative ordering of E1 and E2 can vary from one context switch to the other.

Answer 1

Question Source: Q 16  https://www.cse.iitb.ac.in/~mythili/os/ps/xv6/ps-xv6-proc.pdf

The complete concept is already been discussed here - 

https://www.youtube.com/watch?v=Ywqjv0_uh0U&list=PLIPZ2_p3RNHgz_uIqO3iGfZETeqNAyVUH

$$\begin{align*} & \text{Step A:} \\ & - \text{Saving the context of P1} \\ & - \text{Restoring the context of P2, which includes shifting} \\ & \quad \text{the stack pointer from P1's kernel stack to P2's} \\ & \quad \text{kernel stack.} \\ & \text{Step B:} \\ & - \text{Starting the execution of P2} \\ & - \text{Shifting the program counter to P2's address} \\ & \quad \text{space from P1's address space.} \end{align*}$$