It is a preemptive version of Longest Job First.
Criteria: Burst Time + Arrival Time
Mode: Preemptive
Data Structure: Max Heap
Gantt Chart:
Number of Context Switching (CS) = 19 (Here time required for context switching is expensive)
Now we calculate Turn Around Time (TAT) and Waiting Time (WT) using the following formula:
TAT = CT - AT, WT = TAT – BT
And
Response Time (RT) = FR (First Response) - AR (Arrival Time)
Advantages of LRTF
a. It corrects some of the weaknesses of both SJF and FCFS.
b. It tries to reduce overall turnaround time and maximize system utilization for
height system loads.
Disadvantage
a. Starvation of shorter job.
b. Low response time among several jobs.
Question. (GATE 2006)
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 turnaround time is:
(a) 13 units
(b) 14 units
(c) 15 unit
(d) 16 unit
Answer:
As per question
Gantt Chart:
Now we calculate Turn Around Time (TAT) and Waiting Time (WT) using the following formula:
Turn Around Time = Completion Time - Arrival Time
CT = TAT because AT = 0 for all process
Option (a) correct.