Kernal level vs User level thread

Question

Consider two processes X having P threads and Y having Q threads with equal time slices respectively.Threads are mixed with user level threads (ULT) and kernel level threads (KLT) with P > Q. Now consider the following statements

 
I) If all threads are user level threads (ULT) then Y executes (Q/P) times more faster than X.
II) If all threads are Kernel level threads (KLT) then Y gets (Q/P) times more CPU time than X.
III) If all P are ULT and Q are KLT then X takes more context switching time than Y.

Which of the above statements are TRUE.

1. III only
2. II and III only
3. I and II only
4.I, II and III

 

 

How statement-1 Is true??

Comments

I think none of the statement s true

though $3$ can be true to some extent

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@srestha

III statement is false...

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3^rd can never be true. User level threads are managed by thread library which happens in user space, so context switching happens way faster.

So I feel all are wrong.

Answer 1

None of the statements and none of the options are correct.

Statement-1 is wrong because both processes X and Y will get CPU for the same quantums of time. CPU doesn't know about the user level threads. Then how can anyone one process execute faster?

Statement-2 is wrong. Y gets lesser time than X because P>Q.

Statement-3 is wrong. Y takes more context switching time than X.

Answer 2

You can answer this by eliminating options.

III statement where all P is ULT when X is scheduled switching between threads is register switch which takes lesser time compared to context switch. Q kernel level threads will be scheduled independently of Y and switching between threads is a context switch. So think of it like Q + 1(X) processes to be scheduled on CPU. Therefore it's clear that Y takes more time than X due to context switch for switching between each thread. All options other than 3. contains III, therefore, 3. is the answer.

Answer 3

and statement III is wrong.