Test by Bikram | Operating Systems | Test 2 | Question: 20

Question

Consider a demand-paging system with the following time-measured utilization:

$\begin{array}{ll} \text{COU Utilization} & 20 \% \\ \text{Paging disk} & 97.7 \% \\ \text{Other I/O devices} & 5 \% \end{array}$

Which of the following will probably improve CPU utilization?

• A. Increase the degree of multiprogramming
• B. Add pre paging to the page fetch algorithms
• C. Increase the page size
• D. none of the above

Answer 1

A Increasing degree of multiprogramming will result in more trashing resulting in less CPU utilization.

 B  Add pre paging to the page fetch algorithms The CPU will get more data faster, so it will be more in use. This is only the case if the paging action is amenable to pre fetching (i.e., some of the access is sequential).

 C  Increase the page size Increasing the page size will result in fewer page faults if data is being accessed sequentially. If data access is more or less random, more paging action could ensue because fewer pages can be kept in memory and more data is transferred per page fault. So this change is as likely to decrease utilization as it is to increase it.

Comments

IN C WHAT U MEANT BY  Increasing the page size will result in fewer page faults if data is being accessed sequentially. ?

NO WE USE TLB FOR THAT , AND THEY WILL DECREASE TIME WHETHER YOU SEARCH SEQUENTIALLY OR NOT.

YA IF THE PAGE IS NOT FOUND IN TLB THEN IT LEADS TO MORE TIME WHICH LEADS TO  decrease utilization

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sir, 

answer given here also supports option C

http://cseweb.ucsd.edu/classes/fa10/cse120/hw/hw4-sol.pdf

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@Harsh

For option C ,

it depends how we access pages, either by sequential or random access , it is not a general case .

If it is sequential access then increase CPU utilization as less page fault occur.  Sequentially means in some order like locality of reference .

If it is random access then more page fault hence decrease cpu utilization .

So that's why this option is not considered .

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@bikram sir, what is meant by adding pre pages?