- Consider the V system, and a client that reads a file F sequentially.
The file is not initially cached; the data needs to come from the
disk. The file is 4,000 blocks long. The blocks are not necessarily
arranged sequentially on disk.
Assume that the disk block size for the disks on a file server was
increased by a factor of four. The file size remains the same, the
file is read one block at a time, and, even with the larger block
size, a single ReplyWithSegment is used to transfer the block of data.
In qualitative terms, what would be the effect on the client's
execution time in reading file F (again, not cached)?
- In 1999, Wang et al. proposed a disk drive architecture
supporting a service called "eager write". Rather than update a block
in place, as with normal disks, an eager writing disk simply writes to
the next free block near the disk head (the disk internally keeps
track of this mapping by maintaining a table mapping "logical" disk
blocks to physical disk blocks). Argue whether using such a disk
would improve the performance of a Log-Structured File System, hurt
its performance, or make little difference.
- Many of the papers we have read can be placed into one
of two categories: papers that attempt to virtualize a resource to
provide transparency to the underlying implementation, and papers that
attempt to expose a resource to allow applications to improve their
performance. For the following systems, describe which resource is
virtualized or exposed and what they hoped to accomplish by doing
- Scheduler Activations
- The Hoare Monitors paper describes assertions before and after
the operations wait and signal in terms of the monitor
invariant I and condition B.
(a) Describe similar assertions for wait and
signal using Mesa monitors and briefly explain why.
(b) The Mesa Monitors paper describes how programmers should test and
wait for conditions using Mesa monitors:
while ( ... )
 b.wait 
- "..." means that arbitrary code could be here
-  is immediately before the while loop starts
-  is at the start of the body of the while loop
-  is immediately before the wait, and  immediately after
-  is immediately after the while loop
Considering the code snippet above, create a table with five rows
corresponding to the five placeholders in the code and two columns
corresponding to the invariant I and condition B. For
each entry in the table, write "hold", "!hold", or "unknown" depending
upon what can be assumed about the invariant or condition,
respectively, at each point in the code snippet.
- [Chase] Many implementations of Sun's Network File Service (NFS)
use the following Work Crew scheme on the server side. The server
node's incoming network packet handler places incoming requests on a
shared work queue serviced by a pool of server threads. When a server
thread is idle (ready to handle a new request), it examines the shared
queue. If the queue is empty, the server thread goes to sleep. The
incoming packet handler is responsible for waking up the sleeping
server threads as needed when new requests are available.
(a) Show how to implement the NFS server-side synchronization using a
monitor with Mesa semantics. For this problem you may assume that the
incoming packet handler is a thread rather than an interrupt handler.
(b) Early NFS server implementations used broadcast as a wakeup
primitive for the server threads, because no signal primitive was
available in Unix kernels at that time (around 1985). This was a
common performance problem for early NFS servers. Why is signal more
efficient than broadcast here?