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    SubjectRe: [RFC] New Improved Cleaner Whiter Timer Interface
    Since the ->event interface holds the timerlist_lock across the entire
    ->event call invocation there is no SMP timer add-back race and the
    timer_enter/exit mechanism isn't needed, so more baggage can go. The
    timer_enter/exit is therefore moved off the ->event patch to the legacy
    path. Normal del_timer is all that's needed to delete an ->event style
    timer.

    The only problem with this is, with the timerlist_lock held all the way
    through the ->event execution there is bound to be more contention.
    This is only a temporary problem: run_timer_list is going to be per-cpu
    anyway, with a per-cpu spinlock.

    The (trivially) updated patch:

    --- ../2.4.1.clean/include/linux/timer.h Tue Jan 30 08:24:55 2001
    +++ ./include/linux/timer.h Fri Feb 2 01:02:02 2001
    @@ -22,6 +22,7 @@
    unsigned long expires;
    unsigned long data;
    void (*function)(unsigned long);
    + unsigned long (*event)(unsigned long data);
    };

    extern void add_timer(struct timer_list * timer);
    @@ -49,6 +50,7 @@
    static inline void init_timer(struct timer_list * timer)
    {
    timer->list.next = timer->list.prev = NULL;
    + timer->event = NULL; /* not needed if no ->function */
    }

    static inline int timer_pending (const struct timer_list * timer)
    --- ../2.4.1.clean/kernel/timer.c Sun Dec 10 18:53:19 2000
    +++ ./kernel/timer.c Fri Feb 2 01:02:02 2001
    @@ -299,22 +299,27 @@
    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;
    -
    + if (curr != head) {
    + struct timer_list *timer = list_entry(curr, struct timer_list,
    list);
    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();
    + if (timer->event)
    + {
    + unsigned long requeue = timer->event(timer);
    + if (requeue)
    + {
    + timer->expires = timer_jiffies + requeue;
    + internal_add_timer(timer);
    + }
    + }
    + else
    + {
    + timer_enter(timer);
    + spin_unlock_irq(&timerlist_lock);
    + timer->function(timer->data); /* this should die */
    + spin_lock_irq(&timerlist_lock);
    + timer_exit();
    + }
    goto repeat;
    }
    ++timer_jiffies;
    --
    Daniel
    -
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