Messages in this thread | | | From | "Ulrich Windl" <> | Date | Mon, 21 May 2001 13:51:38 +0200 | Subject | (Fwd) about timer in linux kernel. |
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Maybe one of the people having written the code want to explain...
Thanks, Ulrich ------- Forwarded message follows ------- From: "meng-ju" <mengju@research.att.com> To: <Ulrich.Windl@rz.uni-regensburg.de> Subject: about timer in linux kernel. Date sent: Fri, 18 May 2001 16:58:55 -0700
Hi! Mr. Ulrich Windl, I want to know how timer works in kernel. When we call add_timer(), it will call add_timer_internal to add it to its list. Now I am confused how the system checks if it is expired or not? In run_timer_list(), Why it uses tv1.vec + tv1.index to find out the expiration point while in add_timer_internal(), the expiration timer minus timer_jiffies? I don't understand what roles jiffies, timer_jiffies and tv1.index play. Thanks for your patient and answering. static inline void run_timer_list(void) { spin_lock_irq(&timerlist_lock); while ((long)(jiffies - timer_jiffies) >= 0) { struct list_head *head, *curr; if (!tv1.index) { int n= 1; do { cascade_timers(tvecs[n]); } while (tvecs[n]->index == 1 && ++n < NOOF_TVECS); } repeat: head = tv1.vec + tv1.index; curr = head->next; if (curr != head) { struct timer_list *timer; void (*fn)(unsigned long); unsigned long data;
timer = list_entry(curr, struct timer_list, list); fn = timer->function; data= timer->data;
detach_timer(timer); timer->list.next = timer->list.prev = NULL; timer_enter(timer); spin_unlock_irq(&timerlist_lock); fn(data); spin_lock_irq(&timerlist_lock); timer_exit(); goto repeat; } ++timer_jiffies; tv1.index = (tv1.index + 1) & TVR_MASK; } ........
Meng-Ju
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