Rewrite the scheduler function in xv6 from the default round robin scheduling algorithm into a priority based one

Question

Hello, I have a programming assignment where I have to rewrite the scheduler function in xv6 from the default round robin scheduling algorithm into a priority based one for five different priorities (0x0A - 0x0F). The code is written in C. The entire project can be found at https://github.com/mit-pdos/xv6-riscv.git xv6_p5, and the scheduler function in under kernel/proc.c Please let me know if you can help. Thank you!

Answer 1

I'm not sure if this is what you're looking for. But it would ultimately do what you're asking.

void

scheduler(void)

{

struct proc *p;

struct cpu *c = mycpu();

c->proc = 0;

for(;;) {

// Avoid deadlock by ensuring that devices can interrupt.

intr_on();

// Find the highest priority runnable process

struct proc *high_p = 0;

int highest_priority = 0;

for (p = proc; p < &proc[NPROC]; p++) {

acquire(&p->lock);

if (p->state == RUNNABLE && p->priority > highest_priority) {

highest_priority = p->priority;

high_p = p;

}

release(&p->lock);

}

// Switch to the process with the highest priority

if (high_p != 0) {

acquire(&high_p->lock);

high_p->state = RUNNING;

c->proc = high_p;

swtch(&c->context, &high_p->context);

// Process is done running for now.

// It should have changed its p->state before coming back.

c->proc = 0;

release(&high_p->lock);

}

}

}

In this modified version, we introduce the priority field in the struct proc to store the priority of each process.

The higher the value of priority, the higher the priority of the process.

The scheduler iterates over all processes, acquiring each process's lock to prevent race conditions. It checks if the process is runnable and has a higher priority than the current highest priority found. If so, it updates the high_p variable to point to the new process with the highest priority.

After finding the process with the highest priority, it acquires the lock for that process, sets its state to RUNNING, and switches to its context using the swtch function. Once the process is done running, it releases the lock and continues the loop to find the next highest priority process.

Note that you'll also need to modify other parts of the xv6 codebase, such as the process creation code, to assign appropriate priorities to processes when they are created or modified.