CPU Scheduling

Consider a CPU that has to execute two types of processes. The first type, Actuators (A), requires a CPU burst of 6 seconds. The second type, Controllers (C), requires a CPU burst of 8 seconds. A new process of type A arrives at time $t =$ 10, 20, 30, 40, and 50 (in seconds). Similarly, a new process of type C arrives at time $t =$ 11, 22, 33, 44, and 55 (in seconds). The CPU scheduling policy is First Come First Serve (FCFS). The first process of type A starts running at $t = 10$ seconds. The average waiting time (in seconds) for the 10 processes is ___________. (*rounded off to one decimal place*)

A computer has two processors, $M_1$ and $M_2$. Four processes $P_1, P_2, P_3, P_4$ with CPU bursts of 20, 16, 25, and 10 milliseconds, respectively, arrive at the same time and these are the only processes in the system. The scheduler uses non-preemptive priority scheduling, with priorities decided as follows: • $M_1$ uses priority of execution for the processes as, $P_1 > P_3 > P_2 > P_4$, i.e., $P_1$ and $P_4$ have highest and lowest priorities, respectively. • $M_2$ uses priority of execution for the processes as, $P_2 > P_3 > P_4 > P_1$, i.e., $P_2$ and $P_1$ have highest and lowest priorities, respectively. A process $P_i$ is scheduled to a processor $M_k$, if the processor is free and no other process $P_j$ is waiting with higher priority. At any given point of time, a process can be allocated to any one of the free processors without violating the execution priority rules. Ignore the context switch time. What will be the average waiting time of the processes in milliseconds?

Three processes arrive at time zero with CPU bursts of 16, 20 and 10 milliseconds. If the scheduler has prior knowledge about the length of the CPU bursts, the minimum achievable average waiting time for these three processes in a non-preemptive scheduler (rounded to nearest integer) is __________ milliseconds.

Consider the following CPU processes with arrival times (in milliseconds) and length of CPU bursts (in milliseconds) as given below: $$\begin{array}{|c|c|c|} \hline \text{Process} & \text{Arrival time} & \text{Burst time} \\ \hline P1 & 0 & 7 \\ P2 & 3 & 3 \\ P3 & 5 & 5 \\ P4 & 6 & 2 \\ \hline \end{array}$$ If the pre-emptive shortest remaining time first scheduling algorithm is used to schedule the processes, then the average waiting time across all processes is ________ milliseconds.

Consider an arbitrary set of CPU-bound processes with unequal CPU burst lengths submitted at the same time to a computer system. Which one of the following process scheduling algorithms would minimize the average waiting time in the ready queue?

Consider a uniprocessor system executing three tasks $T_1$, $T_2$ and $T_3$, each of which is composed of an infinite sequence of jobs (or instances) which arrive periodically at intervals of 3, 7 and 20 milliseconds, respectively. The priority of each task is the inverse of its period, and the available tasks are scheduled in order of priority, with the highest priority task scheduled first. Each instance of $T_1$, $T_2$ and $T_3$ requires an execution time of 1, 2 and 4 milliseconds, respectively. Given that all tasks initially arrive at the beginning of the 1st millisecond and task preemptions are allowed, the first instance of $T_3$ completes its execution at the end of _____ milliseconds.

Consider the following set of processes that need to be scheduled on a single CPU. All the times are given in milliseconds. $$\begin{array}{|c|c|c|} \hline \textbf{Process Name} & \textbf{Arrival Time} & \textbf{Execution Time} \\ \hline A & 0 & 6 \\ B & 3 & 2 \\ C & 5 & 4 \\ D & 7 & 6 \\ E & 10 & 3 \\ \hline \end{array}$$ Using the shortest remaining time first scheduling algorithm, the average process turnaround time (in msec) is _____.