Timer

• Time

Wall Time/Real Time

Process Time

Real Start Time

• boot based time

Monotonic Time

• Monotonic time in Mac OS X
  • Monotonic time is a time that increases, well, monotonically from an arbitrary reference point.

• System Timer
  • programmable interrupt timer(PIT)
  • local APIC timer
  • time stamp counter (TSC)

ktimer

• Timer/Dynamic Timer/Kernel Timer
  • Kernel timers are run as the result of a "software interrupt."

• 簡介HZ, tick and jiffies
• kernel/timer.c design

del_timer race conditions

• del_timer_sync
  • deactivate a timer and wait for the handler to finish

• race conditions
  • the timer ends up when the function del_timer is executed.
  • case 1
    • The common problem is deleting timers which restart themselves (by calling add_timer() at the end of their timer function). If del_timer is return before the timer function is finished, then the timer is restarted by the timer function's call to add_timer.
  • case 2
    • If, after deleting the timer, the code went on to free or otherwise manipulate resources used by the timer handler.

• Racing Timers: A Kernel Pastime

Dynamic ticks

• Dynamic Tick Timer for Linux (dyn-tick)

high resolution timer

• high resolution timers project

CPUfreq

• Linux kernel CPUfreq subsystem