Advanced Operating Systems: Lecture 37 - Mr. Farhan Zaidi

Advanced Operating Systems - Lecture 37: Interrupt handlers. This lecture will cover the following: interrupt handlers; interrupts and exceptions; linux interrupt handling; top halfs, bottom halfs and tasklets; timings and timer devices; linux kernel timers and interval timers;...

CS703 ­ Advanced  Operating Systems By Mr Farhan Zaidi Lecture No.  37 Overview of today’s lecture       Interrupt handlers Interrupts and exceptions Linux interrupt handling Top halfs, bottom halfs and tasklets Timings and timer devices Linux kernel timers and interval timers Interrupt Handlers   Interrupt handlers are best hidden  Interrupt procedure does its task Interrupts vs Exceptions  Varying terminology but for Intel:  Interrupt (device generated)  Maskable: device-generated, associated with IRQs (interrupt request lines); may be temporarily disabled (still pending)  Nonmaskable: some critical hardware failures  Exceptions (Processor-detected)  Faults – correctable (restartable); e.g page fault  Traps – no reexecution needed; e.g breakpoint  Aborts – severe error; process usually terminated (by signal)  Programmed exceptions (software interrupts)  int (system call), int3 (breakpoint)  into (overflow), bounds (address check) Interrupts and Exceptions  Hardware support for getting CPUs attention     Often transfers from user to kernel mode Asynchronous: device or timer generated Synchronous: immediate result of last instruction Intel terminology and hardware  Irqs, vectors, IDT, gates, PIC, APIC Interrupt Handling  More complex than exceptions   Some issues:   Requires registry, deferred processing, etc IRQs are often shared; all handlers (ISRs) are executed so they must query device Three types of actions:    Critical: Top-half (interrupts disabled – briefly!) Non-critical: Top-half (interrupts enabled) Non-critical deferrable: Do it “later” (interrupts enabled) Interrupt Handling Components IRQs vector Memory Bus PIC INTR CPU idtr IDT 15 Mask points 255 handler Timing and Timers  Accurate timing crucial for many aspects of OS       Intel timer hardware      Device-related timeouts File timestamps (created, accessed, written) Time-of-day (gettimeofday() High-precision timers (code profiling, etc.) Scheduling, cpu usage, etc RTC: Real Time Clock PIT: Programmable Interrupt Timer TSC: TimeStamp Counter (cycle counter) Local APIC Timer: per-cpu alarms Timer implementations   Kernel timers (dynamic timers) User “interval” timers (alarm(), setitimer())  Dynamic timers may be dynamically created and destroyed No limit is placed on the number of currently active dynamic timers  A dynamic timer is stored in the following timer_list structure: struct timer_list { struct list_head list; unsigned long expires; unsigned long data; void (*function)(unsigned long); }; Software timers in Linux  Each timer contains a field that indicates how far in the future the timer should expire This field is initially calculated by adding the right number of ticks to the current value of jiffies  The field does not change Every time the kernel checks a timer, it compares the expiration field to the value of jiffies at the current moment, and the timer expires when jiffies is greater or equal to the stored value User Mode Interval Timers  setitimer(): distinct user mode interval timers    three timers:     can set for one-time or periodic alarm sends signals on timer expiry ITIMER_REAL: elapsed time (SIGALRM) ITIMER_VIRT: user (SIGVTALRM) ITIMER_PROF: user + kernel (SIGPROF) implementations:   VIRT, PROF – updates by PIT or APIC REAL – requires kernel timer  may need to deliver to blocked process  current->real_timer  shared by alarm() API so can’t use both ... query device Three types of actions:    Critical: Top-half (interrupts disabled – briefly!) Non-critical: Top-half (interrupts enabled) Non-critical deferrable: Do it “later” (interrupts enabled)...       Intel timer hardware      Device-related timeouts File timestamps (created, accessed, written) Time-of-day (gettimeofday() High-precision timers (code profiling, etc.) Scheduling,.. .Lecture? ?No.  37 Overview of today’s? ?lecture       Interrupt handlers Interrupts and exceptions Linux interrupt