Midterm Review
David Ferry, Chris Gill
CSE 522S - Advanced Operating Systems
Washington University in St. Louis
St. Louis, MO 63130
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Exam Scope
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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
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Course Concepts
Kernel execution:
Timing:
– System calls
– Interrupt handlers
– Kernel threads
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Time sources
Timers
Timer granularity
Benchmarking
Kernel Programming:
– Kernel modules
– Core kernel image
Tracing:
– Kernel tracing
– System call tracing
CSE 522S – Advanced Operating Systems
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Course Concepts
Processes:
Kernel Synch:
– Process creation
– Process address space
Scheduling:
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Mutexes
Spinlocks
Deadlock
Race Conditions
O(1) Scheduler
CFS Scheduler
Real-Time Scheduler
Scheduler tensions
CSE 522S – Advanced Operating Systems
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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
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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
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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
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