HZ & jiffies

HZ是用來定義每一秒有幾次timer interrupts(time tick)

jiffies:

the number of time ticks since kernel start

ex:

unsigned long timeout=jiffies+ 3*HZ;

//  the time after 3 second

time_after(jiffies, timeout)

convert from jiffies to seconds

divide by HZ

time related methods:

time_after:  parameter is time tick 

time_before: parameter is time tick

schedule_timeout: parameter is time tick  

only schedule_timeout will give up processor

wait_event_timeout:

msleep: parameter is milliseconds

timer example( do something in the future):

#include

struct timer_list my_timer;

init_timer(&my_timer);            /* Also see setup_timer() */

my_timer.expire = jiffies + n*HZ; /* n is the timeout in number

                                     of seconds */

my_timer.function = timer_func;   /* Function to execute

                                     after n seconds */

my_timer.data = func_parameter;   /* Parameter to be passed

                                     to timer_func */

add_timer(&my_timer);             /* Start the timer */