Homework solution1
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The document describes a problem involving scheduling of processes with I/O and processor usage over multiple time periods, where each process spends half the time period doing I/O and half using the processor, and defines metrics like turnaround time and throughput to compute for different numbers of simultaneous jobs under two scheduling models. It also involves possible process state transitions and determining which are possible or impossible, and suggests an intermediate scheduling policy that balances priority and performance when processes are in the Ready and Ready/Suspend states.
Homework solution1
- 1. Problem 2.1 • Suppose we have a multiprogrammed computer in which each job has identical characteristics. In one computation period, T, for a job, half the time is spent in I/O and the other half in processor activity. Each job runs for a total of N periods. Assume that a simple round-robin scheduling is used, and that I/O operations can overlap with processor operation. Define the following quantities: • Turnaround time = actual time to complete a job • Throughput = average junber of jobs completed per time period T • Processor utilization = percentage of time that the processor is active (not waiting) • Compute these quantities for one, two and four simultaneous jobs, assuming the period T is distributed in each of the following ways: (a) I/O first half, processor second half (b) I/O first and fourth quarter, processor second and fourth quarter.
- 2. Problem 2.1 • Each process uses the first half of the time period T to do IO • Then in second half, uses the processor • Process needs N time periods to complete • One process:
- 3. Problem 2.1 • Each process uses the first half of the time period T to do IO • Then in second half, uses the processor • Process needs N time periods to complete • Two proceses:
- 4. Problem 2.1 • Each process uses the first half of the time period T to do IO • Then in second half, uses the processor • Process needs N time periods to complete • Two procesess:
- 5. Problem 3.3 Possible transitions (pages 123-124): • New → Ready or Ready/Suspend • Ready → Running or Ready/Suspend • Ready/Suspend → Ready • Blocked → Ready or Blocked/Suspend • Blocked/Suspend → Ready /Suspend or Blocked • Running → Ready, Ready/Suspend, or Blocked • Any State → Exit a. List all possible transitions and give an example of what could cause each.
- 6. Problem 3.3 Impossible transitions: • New → Blocked, Blocked/Suspend, or Running: A newly created process remains in the new state until the processor is ready to take on an additional process, at which time it goes to one of the Ready states. • Ready → Blocked or Blocked/Suspend: Typically, a process that is ready cannot subsequently be blocked until it has run. Some systems may allow the OS to block a process that is currently ready, perhaps to free up resources committed to the ready process. • Ready/Suspend → Blocked or Blocked/Suspend: Same reasoning as preceding entry. b. List all impossible transitions and explain why they cannot occur
- 7. Problem 3.3 • Ready/Suspend → Running: The OS first brings the process into memory, which puts it into the Ready state. • Blocked → Ready /Suspend: this transition would be done in 2 stages. A blocked process cannot at the same time be made ready and suspended, because these transitions are triggered by two different causes. • Blocked/Suspend → Ready: same reasoning as Blocked → Ready /Suspend b. List all impossible transitions and explain why they cannot occur
- 8. Problem 3.6 • Consider the transition diagram from the previous problem. Suppose that it is time for the OS to dispatch a process and that there are processes in both the Ready state and the Ready/Suspend state and that at least one process in the Ready/Suspend state has higher scheduling priority than any of the processes in the Ready state. Two extreme policies are as follows: 1. Always dispatch a process in the ready state, to minimize swapping; and 2. Always give preference to the highest priority process , even though that may mean swapping when swapping is not necessary. Suggest an intermediate policy that tries to balance the concerns of priority and performance.
- 9. Problem 3.6 • Penalize the Ready, suspend processes by some fixed amount, such as one or two priority levels • Then a Ready/Suspend process is chosen next only if it has a higher priority than the highest-priority Ready process by several levels of priority.
- 10. Problem 3.6 • Penalize the Ready, suspend processes by some fixed amount, such as one or two priority levels • Then a Ready/Suspend process is chosen next only if it has a higher priority than the highest-priority Ready process by several levels of priority.