1
GATE CSE 2006
+2
-0.6
Consider three processes (process id $$0,1,2,$$ respectively) with compute time bursts $$2, 4,$$ and $$8$$ time units. All processes arrive at time zero. Consider the longest remaining time first $$(LRTF)$$ scheduling algorithm. In $$LRTF$$ ties are broken by giving priority to the process with the lowest process id. The average turn around time is
A
$$13$$ units
B
$$14$$ units
C
$$15$$ units
D
$$16$$ units
2
GATE CSE 2006
+2
-0.6
Consider three processes, all arriving at time zero, with total execution time of $$10,20,$$ and $$30$$ units, respectively. Each process spends the first $$20$$% of execution time doing $${\rm I}/O$$, the next $$70$$% of time doing computation, and the last $$10$$% of time doing $${\rm I}/O$$ again. The operating system uses a shortest remaining compute time first scheduling algorithm and scheduling a new process either when the running processes gets blocked on $${\rm I}/O$$ or when the running process finishes its compute burst. Assume that all $${\rm I}/O$$ operations can be overlapped as much as possible. For what percentage of time does the $$CPU$$ remain idle?
A
$$0$$%
B
$$10.6$$%
C
$$30.0$$%
D
$$89.4$$%
3
GATE CSE 2006
+2
-0.6
The atomic fetch-and-set x, y instruction unconditionally sets the memory location x to 1 and fetches the old value of x n y without allowing any intervening access to the memory location x. consider the following implementation of P and V functions on a binary semaphore S.

void P (binary_semaphore *s) {

unsigned y;
unsigned *x = &(s->value);

do {

fetch-and-set x, y;

} while (y);
}

void V (binary_semaphore *s) {

S->value = 0;

} 
Which one of the following is true?
A
The implementation may not work if context switching is disabled in P
B
Instead of using fetch-and–set, a pair of normal load/store can be used
C
The implementation of V is wrong
D
The code does not implement a binary semaphore
4
GATE CSE 2006
+2
-0.6
Barrier is a synchronization construct where a set of processes synchronizes globally i.e. each process in the set arrives at the barrier and waits for all others to arrive and then all processes leave the barrier. Let the number of processes in the set be three and S be a binary semaphore with the usual P and V functions. Consider the following C implementation of a barrier with line numbers shown on left.
void barrier (void) {
1: P(S);
2: process_arrived++;
3: V(S);
4: while (process_arrived !=3);
5: P(S);
6: process_left++;
7: if (process_left==3) {
8: process_arrived = 0;
9: process_left = 0;
10: }
11: V(S);
}

The variables process_arrived and process_left are shared among all processes and are initialized to zero. In a concurrent program all the three processes call the barrier function when they need to synchronize globally.
Which one of the following rectifies the problem in the implementation?
A
Lines 6 to 10 are simply replaced by process_arrived--
B
At the beginning of the barrier the first process to enter the barrier waits until process_arrived becomes zero before proceeding to execute P(S).
C
Context switch is disabled at the beginning of the barrier and re-enabled at the end.
D
GATE CSE Papers
2023
2022
2020
2019
2018
2013
2012
2011
2010
2009
2008
2007
2006
2005
2004
2003
2002
2001
2000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
EXAM MAP
Medical
NEET