1. Semester Review Chris Gill CSE 422S - Operating Systems Organization
Washington University in St. Louis
St. Louis, MO 63130

2. CSE 522S – Advanced Operating Systems
Semester Exam
8-10 questions, which will test for comprehension, some key terms and details, and a bit of analysis
Studios are useful for analysis & concepts (and familiarity)
Details from slides & readings matter as well
Will cover material throughout the semester
You will be allowed two 8.5 inch by 11 inch pages of notes (with information on one or both sides of each)
Should be readable with your normally corrected vision
Pens, pencils, erasers, water bottles also allowed
No other materials or sources of information (phones off)
80 minutes total, 8:40-10am on Wed Nov 29th
Try to arrive early, in Cupples II L001 (note the location!)
Will distribute exams, start promptly at 8:40am
CSE 522S – Advanced Operating Systems

3. Core Concepts (Pre-Midterm)
Kernel execution
Timing
System calls
Time sources (clocks)
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. Core Concepts (Pre-Midterm)
Processes
Interrupt handling
Process creation
Interrupt context
Process address space
Process context
Process family tree
Top half processing
Bottom half processing
Scheduling
IRQs
Tasklets
O(1) Scheduler
Work queues
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 implementing this feature: syscall vs. kernel module. Give two advantages of implementing this by creating a new system call (4 points): Give two advantages of implementing this by creating a new kernel module that reads and writes files (4 points): If you use the kernel module approach, what must user programs do to pass requests to it after it has been loaded (2 points)?
CSE 522S – Advanced Operating Systems

6. CSE 522S – Advanced Operating Systems
Example Question #2
You have a periodic system where the Linux real-time scheduler runs every ms, the round-robin scheduling interval is 100ms, and there are five tasks, which will consume 300ms, 300ms, 400ms, 500ms, and 700ms of processor time respectively each time they run. If your system schedules tasks in FIFO order on a single core, what is the longest a task might wait before it runs (3 points)? If it instead schedules tasks in round-robin order on a single core, what is the longest a task might wait before it runs (3 points)? Rank the round-robin and FIFO schedulers as as either “HIGH” or “LOW” for each of: response time, overhead, fairness (3 points).
CSE 522S – Advanced Operating Systems

7. CSE 522S – Advanced Operating Systems
Example Question #3
In the blank next to each term below, please write the letter for the text that best matches it and that it best matches (4 points). ___ task structure a. Non-root node of process family tree ___ init process b. Implements process family tree node ___ child process c. Extends process family tree ___ fork call d. Root of the process family tree
CSE 522S – Advanced Operating Systems

8. Core Concepts (Post-Midterm)
Kernel synch
Process address spaces
Mutexes
Virtual memory areas
Memory mapping and unmapping
Spinlocks
Deadlock
Race Conditions
Shared memory
Kernel memory
Only use kernel to map initially and unmap after done
Page level management
Use same physical memory
Object level management
Map to (different) virtual addresses in the processes
Slab allocation
User space memory
CSE 522S – Advanced Operating Systems

9. Core Concepts (Post-Midterm)
VFS layer
Superblocks, filesystems, paths, namespaces, inodes, directory entries
Page cache and writeback
Mapping files into memory
Directory entry hierarchy
Read/write caching
Eviction strategies
Block I/O layer
Flusher threads, writebacks
Character vs. block devices
New bio and bio_vec structures
I/O scheduling
CSE 522S – Advanced Operating Systems

10. CSE 522S – Advanced Operating Systems
Example Question #4
Briefly, why are disk I/O schedulers sometimes called “elevators?” (2 points) Briefly, why do most I/O schedulers merge requests that target adjacent data blocks? (3 points) Briefly, why does Linux cache write requests in memory, rather than always writing them directly back to disk? (3 points)
CSE 522S – Advanced Operating Systems

11. CSE 522S – Advanced Operating Systems
Example Question #5
User-space programs may be linked either statically or dynamically (or a combination of the two). Briefly, when is static linking performed? (2 points) Briefly, when is dynamic linking performed? (2 points) Briefly, what is one advantage of static linking over dynamic linking? (2 points) Briefly, what is one advantage of dynamic linking over static linking? (2 points)
CSE 522S – Advanced Operating Systems

12. CSE 522S – Advanced Operating Systems
Example Question #6
Please circle the letter next to each of the following descriptions that illustrates the idea of “lock data, not code” (4 points).
Put locks around a sequence of reads and writes to same memory location
Make critical sections as long as possible
Lock a data structure when accessing or removing elements
Use spin lock instead of mutex
CSE 522S – Advanced Operating Systems

13. CSE 522S – Advanced Operating Systems
Semester Exam
8-10 questions, which will test for comprehension, some key terms and details, and a bit of analysis
Studios are useful for analysis & concepts (and familiarity)
Details from slides & readings matter as well
Will cover material throughout the semester
You will be allowed two 8.5 inch by 11 inch pages of notes (with information on one or both sides of each)
Should be readable with your normally corrected vision
Pens, pencils, erasers, water bottles also allowed
No other materials or sources of information (phones off)
80 minutes total, 8:40-10am on Wed Nov 29th
Try to arrive early, in Cupples II L001 (note the location!)
Will distribute exams, start promptly at 8:40am
CSE 522S – Advanced Operating Systems