Priority Model

1
Priority Model
2
Thread Priority Process class level
3
Scheduling

• Threads scheduled by executive.
• Priority based preemptive scheduling.

4
Servicing an interrupt
5
Servicing an interrupt
1
Device interrupts
6
Servicing an interrupt
1
Device interrupts
7
Servicing an interrupt
1
2
Device interrupts
Transfer control to ISR
DPC
8
Servicing an interrupt
1
2
Device interrupts
Transfer control to ISR
DPC
9
Servicing an interrupt
1
2
3
Device interrupts
Transfer control to ISR
Stop int.. and queue DPC
10
Servicing an interrupt
1
2
3
Device interrupts
Transfer control to ISR
Stop int.. and queue DPC
Task level drops and DPC can execute
4
11
Servicing an interrupt
1
2
3
Device interrupts
Transfer control to ISR
Stop int.. and queue DPC
5
6
Transfer control to drivers DPC
Execution of DPC routine
Task level drops and DPC can execute
4
12
I/O Handling

• I/O request is sent to device driver.
• Device completes operation and interrupts.
• Complete I/O request.

Buffered I/O
Direct I/O
Users space
Users space
System
System
APC
Device
Device
(Keyboard, mouse)
(disk, network)