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Subject[PATCH 2/4] timer: Provide mod_timer_on()
In order to convert queue_work_on() to mod_timer (so that we can avoid
calling cancel_delayed_work() every time we want to modify a delayed
work) we need to have a mod_timer_on().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
---
include/linux/timer.h | 1
kernel/timer.c | 75 ++++++++++++++++++++++++++++++++------------------
2 files changed, 50 insertions(+), 26 deletions(-)
Index: linux-2.6/include/linux/timer.h
===================================================================
--- linux-2.6.orig/include/linux/timer.h
+++ linux-2.6/include/linux/timer.h
@@ -209,6 +209,7 @@ static inline int timer_pending(const st
extern void add_timer_on(struct timer_list *timer, int cpu);
extern int del_timer(struct timer_list * timer);
extern int mod_timer(struct timer_list *timer, unsigned long expires);
+extern int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu);
extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
extern int mod_timer_pinned(struct timer_list *timer, unsigned long expires);

Index: linux-2.6/kernel/timer.c
===================================================================
--- linux-2.6.orig/kernel/timer.c
+++ linux-2.6/kernel/timer.c
@@ -648,8 +648,8 @@ static struct tvec_base *lock_timer_base
}

static inline int
-__mod_timer(struct timer_list *timer, unsigned long expires,
- bool pending_only, int pinned)
+__mod_timer_on(struct timer_list *timer, unsigned long expires,
+ bool pending_only, int pinned, int cpu)
{
struct tvec_base *base, *new_base;
unsigned long flags;
@@ -673,12 +673,14 @@ __mod_timer(struct timer_list *timer, un

debug_activate(timer, expires);

- cpu = smp_processor_id();
+ if (cpu == -1) {
+ cpu = smp_processor_id();

#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
- if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
- cpu = get_nohz_timer_target();
+ if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
+ cpu = get_nohz_timer_target();
#endif
+ }
new_base = per_cpu(tvec_bases, cpu);

if (base != new_base) {
@@ -705,12 +707,30 @@ __mod_timer(struct timer_list *timer, un
base->next_timer = timer->expires;
internal_add_timer(base, timer);

+ if (cpu != smp_processor_id()) {
+ /*
+ * Check whether the other CPU is idle and needs to be
+ * triggered to reevaluate the timer wheel when nohz is
+ * active. We are protected against the other CPU fiddling
+ * with the timer by holding the timer base lock. This also
+ * makes sure that a CPU on the way to idle can not evaluate
+ * the timer wheel.
+ */
+ wake_up_idle_cpu(cpu);
+ }
out_unlock:
spin_unlock_irqrestore(&base->lock, flags);

return ret;
}

+static inline int
+__mod_timer(struct timer_list *timer, unsigned long expires,
+ bool pending_only, int pinned)
+{
+ return __mod_timer_on(timer, expires, pending_only, pinned, -1);
+}
+
/**
* mod_timer_pending - modify a pending timer's timeout
* @timer: the pending timer to be modified
@@ -826,6 +846,29 @@ int mod_timer_pinned(struct timer_list *
EXPORT_SYMBOL(mod_timer_pinned);

/**
+ * mod_timer_on - modify a timer's timeout and move it to a specific cpu
+ * @timer: the timer to be modified
+ * @expires: new timeout in jiffies
+ * @cpu: cpu to migrate the timer to
+ *
+ * See mod_timer(), equivalent to:
+ *
+ * del_timer(timer); timer->expires = expires; add_timer_on(timer, cpu);
+ *
+ * The function returns whether it has modified a pending timer or not.
+ */
+int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu)
+{
+ if (timer_pending(timer) && timer->expires == expires)
+ return 1;
+
+ expires = apply_slack(timer, expires);
+
+ return __mod_timer_on(timer, expires, false, TIMER_NOT_PINNED, cpu);
+}
+EXPORT_SYMBOL(mod_timer_on);
+
+/**
* add_timer - start a timer
* @timer: the timer to be added
*
@@ -855,28 +898,8 @@ EXPORT_SYMBOL(add_timer);
*/
void add_timer_on(struct timer_list *timer, int cpu)
{
- struct tvec_base *base = per_cpu(tvec_bases, cpu);
- unsigned long flags;
-
- timer_stats_timer_set_start_info(timer);
BUG_ON(timer_pending(timer) || !timer->function);
- spin_lock_irqsave(&base->lock, flags);
- timer_set_base(timer, base);
- debug_activate(timer, timer->expires);
- if (time_before(timer->expires, base->next_timer) &&
- !tbase_get_deferrable(timer->base))
- base->next_timer = timer->expires;
- internal_add_timer(base, timer);
- /*
- * Check whether the other CPU is idle and needs to be
- * triggered to reevaluate the timer wheel when nohz is
- * active. We are protected against the other CPU fiddling
- * with the timer by holding the timer base lock. This also
- * makes sure that a CPU on the way to idle can not evaluate
- * the timer wheel.
- */
- wake_up_idle_cpu(cpu);
- spin_unlock_irqrestore(&base->lock, flags);
+ mod_timer_on(timer, timer->expires, cpu);
}
EXPORT_SYMBOL_GPL(add_timer_on);




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