This chapter introduced the following symbols:
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#include <linux/param.h>,HZ The
HZsymbol specifies the number of clock ticks generated per second.-
volatile unsigned long jiffies The
jiffiesvariable is incremented once for each clock tick; thus it’s incrementedHZtimes per second.-
#include <linux/time.h>,void do_gettimeofday(struct timeval *tv); This function returns the current time. It is not available in version 1.2 of the kernel.
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#include <linux/delay.h>,void udelay(unsigned long usecs); The udelay function delays an integer number of microseconds. It should be used to wait for no longer than one millisecond.
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#include <linux/tqueue.h>,void queue_task(struct tq_struct *task, task_queue *list);,void queue_task_irq(struct tq_struct *task,,task_queue *list);,void queue_task_irq_off(struct tq_struct *task,,task_queue *list); These functions register a task for later execution. The first function, queue_task, can always be called; the second can be called only from non-reentrant functions, and the last one can be called only when interrupts are disabled. Only the first function is available in recent kernels (see Section 17.4 in Chapter 17).
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void run_task_queue(task_queue *list); This function consumes a task queue.
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task_queue tq_immediate, tq_timer, tq_scheduler; These predefined task queues are run as soon as possible, after each timer tick, and before the kernel schedules a new process, respectively.
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#include <linux/timer.h>,void init_timer(struct timer_list * timer); This function initializes a newly allocated
timer.-
void add_timer(struct timer_list * timer); This function inserts the
timerinto the global list of pending timers.-
int del_timer(struct timer_list * timer); del_timer removes a timer from the list of pending timers. If the timer was actually queued, del_timer returns 1, otherwise it returns 0.