report.txt

Roll Number - 20161035
OS Assignment 5

Alternative 1: The Priority Based Scheduler

Comparison between default scheduler of xv6, that is Round Robin and Priority Based Scheduler :-

* Round Robin Scheduler -  It uses time slices also known as time quanta which are assigned to each process in equal portions and in
circular order, handling all processes without priority (also known as cyclic executive). Round-robin scheduling is
simple, easy to implement, and starvation-free.

* Priority Based Scheduler - Priority scheduling involves priority assignment to every process, and processes with higher priorities
 are carried out first, whereas tasks with equal priorities are carried out on round robin basis.

foo.c -> Its forking new processes for testing by doing useless calculations.

for(k=0; k<n; k++)
    {
        id = fork();
        if(id < 0)
            printf(1, "%d failed in fork!\n", getpid());
        else if(id > 0)
        {   // Parent
            printf(1, "Parent %d creating child %d\n", getpid(), id);
            wait();
        }
        else
        {   // Child
            printf(1, "Child %d created\n", getpid());
            for(z=0;z<8000000.0;z+=0.001)
                x = x + 3.14*69.69; // Useless calculations to consume CPU time
            break;
        }
    }
    exit();
}

nice.c -> Its used to set priority according to the mentioned pid.

if(priority<0 || priority>100)
    {
        printf(2, "Invalid priority (0-100)!\n");
        exit();
    }
    printf(1, "pid=%d, pr=%d\n", pid, priority);
    ChangePriority(pid, priority); //changes priority. Defined in proc.cs

    exit();