1. Midterm Review David Ferry, Chris Gill
CSE 522S - Advanced Operating Systems
Washington University in St. Louis
St. Louis, MO 63130

2. CSE 522S – Advanced Operating Systems
Exam Scope
Questions derived from slides
Split between comprehension and analysis
Studios useful for analysis & concepts
9 questions
81 minutes
9 minutes per question
Does not cover “details” slides (i.e. boot process and program execution)
CSE 522S – Advanced Operating Systems

3. CSE 522S – Advanced Operating Systems
Course Concepts
Kernel execution:
Timing:
System calls
Time sources
Interrupt handlers
Timers
Kernel threads
Timer granularity
Benchmarking
Kernel Programming:
Tracing:
Kernel modules
Core kernel image
Kernel tracing
System call tracing
CSE 522S – Advanced Operating Systems

4. CSE 522S – Advanced Operating Systems
Course Concepts
Processes:
Kernel Synch:
Process creation
Mutexes
Process address space
Spinlocks
Deadlock
Race Conditions
Scheduling:
O(1) Scheduler
CFS Scheduler
Real-Time Scheduler
Scheduler tensions
CSE 522S – Advanced Operating Systems

5. CSE 522S – Advanced Operating Systems
Example Question #1
Imagine you are implementing a new OS feature that communicates with user space. User programs request an action from the kernel, and the kernel returns some data. Consider two options for the interface: Give two advantages of implementing a new system call (4 points): Give two advantages of using a kernel module that reads and writes files (4 points): If you decide to use a kernel module. What must end users do in order to use your future software patches (2 points)?
CSE 522S – Advanced Operating Systems

6. CSE 522S – Advanced Operating Systems
Example Question #2
You have a periodic system where the scheduler is invoked every 1ms to reschedule tasks, and your system has five tasks, which will consume 3ms, 3ms, 4ms, 5ms, and 7ms of processor time. Suppose your system schedules tasks in FIFO order, what is the longest a task might wait before being scheduled (4 points)? Suppose your system schedules tasks in round-robin order, what is the longest a task might wait before being scheduled (4 points)? Rank the round-robin and FIFO schedulers as as either “HIGH” or “LOW” for each of: response time, overhead, fairness (6 points).
CSE 522S – Advanced Operating Systems

7. CSE 522S – Advanced Operating Systems
Example Question #3
Suppose you’re writing a new feature with a shared data structure. For each of the situations below, say whether to use a mutex or a spinlock and argue why (3 points each):
A large data structure that takes a long time to process.
After your lock, accessing the structure requires taking a separate mutex lock.
The data structure will be accessed from interrupt context.
Why should you disable interrupts when accessing a spinlock that is also used by interrupt handlers (3 points)?
CSE 522S – Advanced Operating Systems