. , .
CPU / I-O -.
. 11.1. -.
. 11.2. .
, , , , .. .
, , , .
, :
1. .
2. .
3. .
4. .
1 4 (non-preemptive).
2 3 (preemptive).
, , . :
.
() (dispatch latency) , , . , , .
, .
(CPU utilization) . : .
(throughput) () , . : .
(turnaround time) , - . : .
(waiting time) , , . : .
(response time) , ( , 1, ). : .
|
|
, , . , .
First-Come-First-Served (FCFS)
First-Come-First-Served ( ) , () , , , , . (Gantt charts , .
. P1, P2 P3 :
P1 | |
P2 | |
P3 |
FCFS , , .
. 11.3. FCFS ( 1).
, P1 = 0; P2= 24; P3 = 27.
: (0 + 24 + 27)/3 = 17.
: P2, P3, P1 ( ), .
. 11.4. FCFS ( 2).
: P1 = 6; P2 = 0; P3 = 3.
: (6 + 0 + 3)/3 = 3
, .
, , (convoy effect) , .
Shortest Job First (SJF)
ShortestJobFirst (SJF, ) , .
. , .
:
1. , , .
2. , , , - . Shortest-Remaining-Time-First (SRTF).
, SJF , , .
SJF . , :
P1 | 0.0 | |
P2 | 2.0 | |
P3 | 4.0 | |
P4 | 5.0 | |
|
|
. 11.5. SJF .
= (0 + 6 + 3 + 7)/4 = 4.
SJF , .
. 11.6. SJF .
:
2 1 2;
4 2 3.
, , , .
= (9 + 1 + 0 +2)/4 = 3, .. , , , .
. . . :
tn n- ;
n- .
tn :
.
0 1. , .
. 11.7. .
, .. .
.. .
, :
.
1, , .