Process scheduling

Question

Consider the following preemptive priority-scheduling algorithm based on dynamically changing priorities. Larger priority numbers imply higher priority. When a process is waiting for the CPU (in the ready queue but not running), its priority changes at a rate X when it is running, its priority changes at a rate Y. All processes are given a priority of 0 when they enter the ready queue. The parameters and can be set to give many different scheduling algorithms. What is the algorithm that results from Y>X>0?

a. LIFO

b. FCFS

c. Round Robin

d. None of the above

Comments

It should be FCFS because  for a particular process if we want to change its priority at higher rate , then we should let the process to execute to its max burst time which will maintain relation Y >X >0
and as we know FCFS is non premptive it will allow the process to execute completely which will maintain relation Y >X >0
but if i choose for LIFo then whatever be last process ( with longer or shorter Cpu burst time ) it need to be excuted by we would be unable to increase the priority of any 1  process . as soon as new process come we have to take that . this may not full fill relation Y >X>O

am i correct in my explanation ?

Answer 1

It should be FCFS. Although I'[m ASSUMING that -  when question says priority is changing, it implies the change is positive - i.e. priority is increasing.

Consider that a process is running and its priority is increasing at rate of Y . Now another process arrives and waits in a queue at time t0. 

At time t1, priority of process which is running would be (t1-t0) * Y while the one which is waiting would be (t1-t0) * X. 

Since Y > X, running process will always have a higher priority. SO the process in queue continues to wait .

So the best answer would be FCFS.

 

 

 

Comments

It can be simply the priority scheduling algo , if all process arrival time is 0

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Y <X<0 then it is LIFO

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When LIFO is Correct ?? @nlkhll1008

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How it is possible??

Answer 2

 

problem 5 of the link below==>>

https://www.cs.utexas.edu/~lorenzo/corsi/cs372/06F/hw/9sol.html    

 

***do check other problems also