linux.conf.au, January 2003
      PRACTICALITIES: More Common Functions

HZ & jiffies
jiffies is a running time counter
Every second, it increases HZ time (1000 on 2.5 x86)
struct timer
add_timer( ) & del_timer_sync( )
Set up and delete a timer to call soon.
Timer runs as soft interrupt, so CANNOT sleep.

struct completion: DECLARE_COMPLETION( )/init_completion( )
wait_for_completion(struct completion *)
Simple version of wait_event: sleep until we get woken.
complete(struct completion *)
Wake up the all the wait_for_completion() sleepers.