CS 423 Operating System Design: Interrupts Professor Adam Bates - - PowerPoint PPT Presentation
CS 423 Operating System Design: Interrupts Professor Adam Bates CS423: Operating Systems Design Goals for Today Learning Objectives: Understand the role and types of of Interrupts Announcements: C4 weekly summaries! Due
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Program Counter Program instructions Code Segment Offset Heap Data Segment Offset
Operand
Data Operand Current Instruction
OpCode
Stack Segment Offset Stack Pointer Stack Registers
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Program Counter Program instructions Code Segment Offset Heap Data Segment
Operand
Data Operand
OpCode
Stack Segment Stack Pointer Registers Stack Program Counter Program instructions Code Segment Offset Heap Data Segment
Operand
Data Operand
OpCode
Stack Segment Stack Pointer Stack
Save State (Context) Load State (Context)
Registers
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The state for processes that are not running on the CPU are maintained in the Process Control Block (PCB) data structure
Updated during context switch
An alternate PCB diagram
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The Hardware (CPU) “Virtual” CPU “Virtual” CPU “Virtual” CPU
Context Switching + Scheduling
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The Hardware (CPU) “Virtual” CPU
Context Switching + Scheduling
“Virtual” CPU “Virtual” CPU External Devices Interrupt Handler Interrupt Handler Interrupt Handler
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Program Counter Program instructions Code Segment Offset Stack Segment Stack Pointer Stack Program Counter Program instructions Code Segment Offset Stack Segment Stack Pointer Stack
Save PC on thread stack Jump to Interrupt handler Handler
(SP, registers, segment pointers, …)
Thread Control Block Thread Control Block
Registers Registers
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Program Counter Program instructions Code Segment Offset Stack Segment Stack Pointer Registers Stack Program Counter Program instructions Code Segment Offset Stack Segment Stack Pointer Registers Stack
Save PC on thread stack Jump to yield() function yield()
(SP, registers, segment pointers, …)
Thread Control Block Thread Control Block
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Interrupt Vector Processor Register
h a n d l e Ti m e r I n t e r r u p t ( ) { . . . } h a n d l e D i v i d e B y Z e r o ( ) { . . . } h a n d l e S y s t e m C a l l ( ) { . . . }
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User Stack Kernel Stack
Proc2 Running Proc1 Main Proc2 Ready to Run Proc1 Main User CPU State User CPU State Syscall Handler I/O Driver Top Half Proc2 Syscall Waiting for I/O Proc1 Main
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■ Hardware generated:
■ Different I/O devices are connected to different
■ Device hardware signals the corresponding line ■ Interrupt controller signals the CPU (by signaling the
■ CPU saves return address after next instruction and
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■ Hardware devices may need asynchronous and
■ Timer interrupt: Timers and time-dependent activities need
to be updated with the passage of time at precise intervals
■ Network interrupt: The network card interrupts the CPU
when data arrives from the network
■ I/O device interrupt: I/O devices (such as mouse and
keyboard) issue hardware interrupts when they have input (e.g., a new character or mouse click)
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LINTx — lines/pins for hardware interrupts. In this case… LINT0 — line for unmaskable interrupts LINT1 — line for maskable interrupts
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■ How are interrupts handled on multicore machines?
■ On x86 systems each CPU gets its own local Advanced
■ The OS can program the APICs to determine which
■ The default (unless OS states otherwise) is to route all
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HALT START Fetch next instruction Execute Instruction
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HALT START Fetch next instruction Execute Instruction
interrupts disabled
Check for INT, init INT handler
Interrupt Stage Execute Stage Fetch Stage
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Hardware
Device controller or other hardware issues an interrupt. Processor finishes execution
P r o c e s s o r s i g n a l s acknowledgment of interrupt. Processor pushes PSW and PC onto stack.
Software
Save remainder of state information. Process interrupt. R e s t o r e p r o c e s s s t a t e information. Restore old PSW and PC. Processor loads new PC value based on interrupt.
Program Status Word (PSW) contains interrupt masks, privilege states, etc.
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■ Software Interrupts:
■ Interrupts caused by the execution of a software
■ INT <interrupt_number>
■ Used by the system call interrupt()
■ Initiated by the running (user level) process ■ Cause current processing to be interrupted and
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■ Exceptions
■ Initiated by processor hardware itself ■ Example: divide by zero
■ Like a software interrupt, they cause a transfer
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■ Interrupts (as the name suggests) have the
■ What are the implications on regular program
■ Must keep interrupt code short in order not to keep
■ Cannot block (regular processing does not resume until
interrupt returns, so if the interrupt blocks in the middle the system “hangs”)
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■ Can an interrupt handler use malloc()? ■ Can an interrupt handler write data to disk? ■ Can an interrupt handler use busy wait?
■ E.G. — while (!event) loop;
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■ Since the interrupt handler must be minimal, all other
■ Example:
■ Network interrupt causes packet to be copied from network card ■ Other processing on the packet should be deferred until its time
comes
■ The deferred portion of interrupt processing is called
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■ Method for deferring portion of interrupt processing ■ Globally serialized ■ When one bottom half is executing, no other bottom
■ Obvious performance limitations; primarily available for
■ Note: other mechanisms for deferred work are also
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■ Handlers that, like bottom halves, must be statically defined/
allocated in the Linux kernel at compile time.
■ A hardware interrupt handler (before returning) uses
raise_softirq() to mark that a given soft_irq must execute deferred work
■ At a later time, when scheduling permits, the marked
soft_irq handler is executed
■ When a hardware interrupt is finished ■ When a process makes a system call ■ When a new process is scheduled
■ Unlike bottom halves, softirqs are reentrant and can be
executed concurrently on several CPUs
■ How to protect data??
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■ HI_SOFTIRQ ■ TIMER_SOFTIRQ ■ NET_TX_SOFTRQ ■ NET_RX_SOFTIRQ ■ BLOCK_SOFTIRQ ■ TASKLET_SOFTIRQ ■ SCHED_SOFTIRQ ■ …
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■ HI_SOFTIRQ ■ TIMER_SOFTIRQ ■ NET_TX_SOFTRQ ■ NET_RX_SOFTIRQ ■ BLOCK_SOFTIRQ ■ TASKLET_SOFTIRQ ■ SCHED_SOFTIRQ ■ …
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■ Another Deferred work mechanism multiplexed on top
■ Scheduled using
■ tasklet_schedule() ■ tasklet_hi_schedule()
■ Typically, a tasklet is serialized with respect to itself. ■ Non-reentrant == easier to code ■ Different task lets can be executed concurrently on
■ Tasklets can be created or removed dynamically ■ Cannot sleep (cannot save their context)
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■
A different mechanism for (non-interrupt) deferred work
■
Work deferred to its own thread
■ Does not run in interrupt concept ■
Can be scheduled together with other threads according to priorities set by a scheduling policy
■
Associated with its thread control block and hence can block (and save context)
■
DECLARE_WORK(name, void (*func)(void *), void *data);
■
INIT_WORK(struct work_struct *work, void (*func)(void *), void *data);
■
schedule_work(&work);