מערכות הפעלה

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:

1

שאלה #43727

		13 units
		14 units
		15 units
		16 units

Let the processes be p0, p1 and p2. These processes will be executed in following order. p2 p1 p2 p1 p2 p0 p1 p2 p0 p1 p2 0 4 5 6 7 8 9 10 11 12 13 14 Turn around time of a process is total time between submission of the process and its completion. Turn around time of p0 = 12 (12-0) Turn around time of p1 = 13 (13-0) Turn around time of p2 = 14 (14-0) Average turn around time is (12+13+14)/3 = 13.

מיין לפי

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 I/O, the next 70% of time doing computation, and the last 10% of time doing I/O again. The operating system uses a shortest remaining compute time first scheduling algorithm and schedules a new process either when the running process gets blocked on I/O or when the running process finishes its compute burst. Assume that all I/O operations can be overlapped as much as possible. For what percentage of time does the CPU remain idle?

1

שאלה #43728

		0%
		10.6%
		30.0%
		89.4%

Let three processes be p0, p1 and p2. Their execution time is 10, 20 and 30 respectively. p0 spends first 2 time units in I/O, 7 units of CPU time and finally 1 unit in I/O. p1 spends first 4 units in I/O, 14 units of CPU time and finally 2 units in I/O. p2 spends first 6 units in I/O, 21 units of CPU time and finally 3 units in I/O. idle p0 p1 p2 idle 0 2 9 23 44 47 Total time spent = 47 Idle time = 2 + 3 = 5 Percentage of idle time = (5/47)*100 = 10.6 %