Final Exam. May 8, 2001. Question 1 -- Answers and Grading
9 points total
Answer
When the paging device is nearly 100 percent, and the CPU is languishing
at 20 percent, our system is thrashing. Given that, all of the answers
should be clear.
- a. No. The CPU is already underutilized. A faster CPU
is simply going to be further underutilized.
- b. No. The problem with this system is too much
paging, not a lack of paging space. This will have no effect on the
CPU utilization.
- c. No. Increasing the degree of multiprogramming means
adding more processes. This is going to futher stress main memory and
cause even more paging activity. This will drop CPU utilization even
further.
- d. Yes. This is straight from the book. We can reduce
the stress on main memory by kicking a few processes out, and therefore
(hopefully) fitting all of the resident processes' working sets into
main memory.
- e. Yes. Again, this should (but may not) decrease the
number of page faults by allowing more of the resident processes' working
sets to be in memory. This will result in an increase of CPU utilization.
- f. Yes, but not by much. Certainly, since the paging
device is being maxed out, getting a faster one should get the pages in
and out faster, thus allowing the CPU to get more work done. But since
disks are extremely slow compared to CPU's, this is not going to improve
performance a huge amount.
Grading
Each part was worth 1.5 points. There were two problems that many of
you had. First was in part b -- many of you assumed that
``bigger'' meant ``faster,'' and got that part incorrect.
The second problem was that many of you said ``yes'' for c, and
then proceeded to say only if the system is not thrashing. That got
you half credit only, because while correct, the system is
thrashing. Similarly, you got half credit for saying ``no'' to
d and then saying that is only if the system is not thrashing.