Scheduling is the method by which threads or processes are given access to system resources (e.g. processor time). Scheduling is usually concerned with load balancing a system effectively to achieve a target quality of service. Fair-share scheduling (FSS) is a scheduling strategy for computer operating systems in which the CPU usage is equally distributed among system users or groups, as opposed to equal distribution among processes.
For Project 5, you are to add a fair-share scheduler to your OS.
The following are important guidelines for the FSS exercise:
Fair-share scheduling is a scheduling strategy for computer operating systems in which the CPU usage is equally distributed among system users or groups, as opposed to equal distribution among processes.
For example, if four users (A,B,C,D) are concurrently executing one process each, the scheduler will logically divide the available CPU cycles such that each user gets 25% of the whole (100% / 4 = 25%). If user B starts a second process, each user will still receive 25% of the total cycles, but each of user B's processes will now use 12.5%. On the other hand, if a new user starts a process on the system, the scheduler will reapportion the available CPU cycles such that each user gets 20% of the whole (100% / 5 = 20%).
Another layer of abstraction allows us to partition users into groups, and apply the fair share algorithm to the groups as well. In this case, the available CPU cycles are divided first among the groups, then among the users within the groups, and then among the processes for that user. For example, if there are three groups (1,2,3) containing three, two, and four users respectively, the available CPU cycles will be distributed as follows:
100% / 3 groups = 33.3% per group
Group 1: (33.3% / 3 users) = 11.1% per user
Group 2: (33.3% / 2 users) = 16.7% per user
Group 3: (33.3% / 4 users) = 8.3% per user
There are 6 points possible for Project 5. The grading criteria will be as follows:
1 pt The P5 command dynamically switches between schedulers. 3 pts Only tasks in the Ready Queue with a non-zero time are scheduled. When all tasks in the Ready Queue have a zero time, then new task times are calculated in a "fair" way. 1 pt Tasks are grouped according to their parent task. Group counts are approximately the same. 1 pt Parents share in clock time with their children. Fractional clocks are given to the parent. -1 pt Penalty for each school day late.
In addition, after completing the above requirements, the following bonus points may be awarded:
+1 pt Pass-off lab at least one day before due date. +2 pts Your fair scheduler works with dead ancestors.
NOTE: Bonus points may be received anytime before the due date of the next project (regardless of any late penalties) as long as all the project requirements have been completed.