XV6 Lottery Scheduler

We added a lottery ticket scheduler, in addition to the default scheduler found on xv6. In this scheduling, every process have some tickets and scheduler picks a random ticket and process having that ticket is the winner and it is executed for a time slice and then another ticket is picked by the scheduler. These tickets represent the share of processes. A process having a higher number of tickets give it more chance to get chosen for execution.

Lottery Scheduling

Essential System Calls

settickets system call:

settickets system call sets the number of tickets for the current process with the following prototype:

int settickets(int number)

getprocessinfo system call:

getprocessesinfo is a system call with the following prototype

int getprocessesinfo(struct processes_info *p);

where struct processses_info is defined in a new header file processesinfo.h as:

struct processes_info {
    int num_processes;
    int pids[NPROC];       
    int times_scheduled[NPROC];
    int tickets[NPROC];               
};

The system call should fill in the struct pointed to by its arguments by:

• setting num_processes to the total number of non-UNUSED processes in the process table

• for each i from 0 to num_processes, setting: pids[i] to the pid of ith non-UNUSED process in the process table;

• times_scheduled[i] to the number of times this process has been scheduled since it was created.

• tickets[i] to the number of tickets assigned to each process.

Building and Running XV6

$ make qemu 

Testing the system call with our user program:

$ testtickets

Testing the lottery scheduler with our user program:

$ lotterytest