CSE 221: Homework 3
Hardcopy due Tuesday, December 5 at the start of class
Answer the following questions. For questions asking for short
answers, there may not necessarily be a "right" answer, although some
answers may be more compelling and/or much easier to justify. But I
am interested in your explanation (the "why") as much as the answer
itself. Also, do not use shorthand: write your answers using complete
When grading homeworks, we will grade one question in detail and
assign full credit for technical answers to the others.
- The Scheduler Activations paper states that deadlock is
potentially an issue when activations perform an upcall:
"One issue we have not yet addressed is that a user-level thread could
be executing in a critical section at the instant when it is blocked
or preempted...[a] possible ill effect ... [is] deadlock (e.g., the
preempted thread could be holding a lock on the user-level thread
ready list; if so, deadlock would occur if the upcall attempted to
place the preempted thread onto the ready list)." (p. 102)
Why is this not a concern with standard kernel threads, i.e., why
do scheduler activations have to worry about this deadlock issue, but
standard kernel threads implementations do not have to?
A reliability-induced synchronous write is a synchronous write
that is issued by the file system to ensure that the file system's
state (as represented by the system's metadata) is not left
inconsistent if the system crashes at an inconvenient time.
- Let f be a new file created in a directory d. The
file system will issue at least three disk operations to complete
this operation. Ignoring any data blocks allocated for the directory
or new file, what are these three disk operations for?
- In Unix FFS, at least two of these writes will be issued
synchronously. Which are they, and what order should they be
performed in? Briefly explain why.
- Consider the Soft Updates solution to this problem. Does it do
any reliability-induced synchronous writes? If so, how does it
differ from FFS? If not, why can it avoid doing so? Explain.
- Consider the same operation in LFS. Does LFS generate any
reliability-induced synchronous writes? Explain.
- Consider the same operation with the Rio file cache. Does Rio
generate any reliability-induced synchronous writes? Explain.
- Both the BN-RPC and IX systems include a variety of optimizations
to improve communication performance. For each of the
optimizations from BN-RPC below:
- State whether IX also optimized this aspect of the system.
- If IX did not optimize it, explain why.
- If IX did optimize it, compare and contrast IX's optimization
relative to BN-RPC. Also, if the papers report the performance
benefits of the optimization, quote the performance results
- Frequent vs. infrequent requests
- Connection management
- Process/thread management
- Communication protocol