timers: add mod_timer_pending()

Impact: new timer API

Based on an idea from Martin Josefsson with the help of
Patrick McHardy and Stephen Hemminger:

introduce the mod_timer_pending() API which is a mod_timer()
offspring that is an invariant on already removed timers.

(regular mod_timer() re-activates non-pending timers.)

This is useful for the networking code in that it can
allow unserialized mod_timer_pending() timer-forwarding
calls, but a single del_timer*() will stop the timer
from being reactivated again.

Also while at it:

- optimize the regular mod_timer() path some more, the
  timer-stat and a debug check was needlessly duplicated
  in __mod_timer().

- make the exports come straight after the function, as
  most other exports in timer.c already did.

- eliminate __mod_timer() as an external API, change the
  users to mod_timer().

The regular mod_timer() code path is not impacted
significantly, due to inlining optimizations and due to
the simplifications.

Based-on-patch-from: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Patrick McHardy <kaber@trash.net>
Cc: netdev@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/powerpc/platforms/cell/spufs/sched.c b/arch/powerpc/platforms/cell/spufs/sched.c
index 6a0ad19..f085369 100644 (file)
--- a/arch/powerpc/platforms/cell/spufs/sched.c
+++ b/arch/powerpc/platforms/cell/spufs/sched.c
@@ -508,7 +508,7 @@ static void __spu_add_to_rq(struct spu_context *ctx)
                list_add_tail(&ctx->rq, &spu_prio->runq[ctx->prio]);
                set_bit(ctx->prio, spu_prio->bitmap);
                if (!spu_prio->nr_waiting++)
-                       __mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);
+                       mod_timer(&spusched_timer, jiffies + SPUSCHED_TICK);
        }
 }
 

diff --git a/drivers/infiniband/hw/ipath/ipath_driver.c b/drivers/infiniband/hw/ipath/ipath_driver.c
index 69c0ce3..cb9daa6 100644 (file)
--- a/drivers/infiniband/hw/ipath/ipath_driver.c
+++ b/drivers/infiniband/hw/ipath/ipath_driver.c
@@ -2715,7 +2715,7 @@ static void ipath_hol_signal_up(struct ipath_devdata *dd)
  * to prevent HoL blocking, then start the HoL timer that
  * periodically continues, then stop procs, so they can detect
  * link down if they want, and do something about it.
- * Timer may already be running, so use __mod_timer, not add_timer.
+ * Timer may already be running, so use mod_timer, not add_timer.
  */
 void ipath_hol_down(struct ipath_devdata *dd)
 {
@@ -2724,7 +2724,7 @@ void ipath_hol_down(struct ipath_devdata *dd)
        dd->ipath_hol_next = IPATH_HOL_DOWNCONT;
        dd->ipath_hol_timer.expires = jiffies +
                msecs_to_jiffies(ipath_hol_timeout_ms);
-       __mod_timer(&dd->ipath_hol_timer, dd->ipath_hol_timer.expires);
+       mod_timer(&dd->ipath_hol_timer, dd->ipath_hol_timer.expires);
 }
 
 /*
@@ -2763,7 +2763,7 @@ void ipath_hol_event(unsigned long opaque)
        else {
                dd->ipath_hol_timer.expires = jiffies +
                        msecs_to_jiffies(ipath_hol_timeout_ms);
-               __mod_timer(&dd->ipath_hol_timer,
+               mod_timer(&dd->ipath_hol_timer,
                        dd->ipath_hol_timer.expires);
        }
 }

diff --git a/include/linux/timer.h b/include/linux/timer.h
index daf9685..e2d662e 100644 (file)
--- a/include/linux/timer.h
+++ b/include/linux/timer.h
@@ -86,8 +86,8 @@ static inline int timer_pending(const struct timer_list * timer)
 
 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(struct timer_list *timer, unsigned long expires);
+extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
 
 /*
  * The jiffies value which is added to now, when there is no timer
@@ -146,25 +146,7 @@ static inline void timer_stats_timer_clear_start_info(struct timer_list *timer)
 }
 #endif
 
-/**
- * add_timer - start a timer
- * @timer: the timer to be added
- *
- * The kernel will do a ->function(->data) callback from the
- * timer interrupt at the ->expires point in the future. The
- * current time is 'jiffies'.
- *
- * The timer's ->expires, ->function (and if the handler uses it, ->data)
- * fields must be set prior calling this function.
- *
- * Timers with an ->expires field in the past will be executed in the next
- * timer tick.
- */
-static inline void add_timer(struct timer_list *timer)
-{
-       BUG_ON(timer_pending(timer));
-       __mod_timer(timer, timer->expires);
-}
+extern void add_timer(struct timer_list *timer);
 
 #ifdef CONFIG_SMP
   extern int try_to_del_timer_sync(struct timer_list *timer);

diff --git a/kernel/relay.c b/kernel/relay.c
index 9d79b78..8f2179c 100644 (file)
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -750,7 +750,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
                         * from the scheduler (trying to re-grab
                         * rq->lock), so defer it.
                         */
-                       __mod_timer(&buf->timer, jiffies + 1);
+                       mod_timer(&buf->timer, jiffies + 1);
        }
 
        old = buf->data;

diff --git a/kernel/timer.c b/kernel/timer.c
index 13dd64f..9b77fc9 100644 (file)
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -589,11 +589,14 @@ static struct tvec_base *lock_timer_base(struct timer_list *timer,
        }
 }
 
-int __mod_timer(struct timer_list *timer, unsigned long expires)
+static inline int
+__mod_timer(struct timer_list *timer, unsigned long expires, bool pending_only)
 {
        struct tvec_base *base, *new_base;
        unsigned long flags;
-       int ret = 0;
+       int ret;
+
+       ret = 0;
 
        timer_stats_timer_set_start_info(timer);
        BUG_ON(!timer->function);
@@ -603,6 +606,9 @@ int __mod_timer(struct timer_list *timer, unsigned long expires)
        if (timer_pending(timer)) {
                detach_timer(timer, 0);
                ret = 1;
+       } else {
+               if (pending_only)
+                       goto out_unlock;
        }
 
        debug_timer_activate(timer);
@@ -629,42 +635,28 @@ int __mod_timer(struct timer_list *timer, unsigned long expires)
 
        timer->expires = expires;
        internal_add_timer(base, timer);
+
+out_unlock:
        spin_unlock_irqrestore(&base->lock, flags);
 
        return ret;
 }
 
-EXPORT_SYMBOL(__mod_timer);
-
 /**
- * add_timer_on - start a timer on a particular CPU
- * @timer: the timer to be added
- * @cpu: the CPU to start it on
+ * mod_timer_pending - modify a pending timer's timeout
+ * @timer: the pending timer to be modified
+ * @expires: new timeout in jiffies
  *
- * This is not very scalable on SMP. Double adds are not possible.
+ * mod_timer_pending() is the same for pending timers as mod_timer(),
+ * but will not re-activate and modify already deleted timers.
+ *
+ * It is useful for unserialized use of timers.
  */
-void add_timer_on(struct timer_list *timer, int cpu)
+int mod_timer_pending(struct timer_list *timer, unsigned long expires)
 {
-       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_timer_activate(timer);
-       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);
+       return __mod_timer(timer, expires, true);
 }
+EXPORT_SYMBOL(mod_timer_pending);
 
 /**
  * mod_timer - modify a timer's timeout
@@ -688,9 +680,6 @@ void add_timer_on(struct timer_list *timer, int cpu)
  */
 int mod_timer(struct timer_list *timer, unsigned long expires)
 {
-       BUG_ON(!timer->function);
-
-       timer_stats_timer_set_start_info(timer);
        /*
         * This is a common optimization triggered by the
         * networking code - if the timer is re-modified
@@ -699,12 +688,62 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
        if (timer->expires == expires && timer_pending(timer))
                return 1;
 
-       return __mod_timer(timer, expires);
+       return __mod_timer(timer, expires, false);
 }
-
 EXPORT_SYMBOL(mod_timer);
 
 /**
+ * add_timer - start a timer
+ * @timer: the timer to be added
+ *
+ * The kernel will do a ->function(->data) callback from the
+ * timer interrupt at the ->expires point in the future. The
+ * current time is 'jiffies'.
+ *
+ * The timer's ->expires, ->function (and if the handler uses it, ->data)
+ * fields must be set prior calling this function.
+ *
+ * Timers with an ->expires field in the past will be executed in the next
+ * timer tick.
+ */
+void add_timer(struct timer_list *timer)
+{
+       BUG_ON(timer_pending(timer));
+       mod_timer(timer, timer->expires);
+}
+EXPORT_SYMBOL(add_timer);
+
+/**
+ * add_timer_on - start a timer on a particular CPU
+ * @timer: the timer to be added
+ * @cpu: the CPU to start it on
+ *
+ * This is not very scalable on SMP. Double adds are not possible.
+ */
+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_timer_activate(timer);
+       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);
+}
+
+/**
  * del_timer - deactive a timer.
  * @timer: the timer to be deactivated
  *
@@ -733,7 +772,6 @@ int del_timer(struct timer_list *timer)
 
        return ret;
 }
-
 EXPORT_SYMBOL(del_timer);
 
 #ifdef CONFIG_SMP
@@ -767,7 +805,6 @@ out:
 
        return ret;
 }
-
 EXPORT_SYMBOL(try_to_del_timer_sync);
 
 /**
@@ -796,7 +833,6 @@ int del_timer_sync(struct timer_list *timer)
                cpu_relax();
        }
 }
-
 EXPORT_SYMBOL(del_timer_sync);
 #endif
 
@@ -1268,7 +1304,7 @@ signed long __sched schedule_timeout(signed long timeout)
        expire = timeout + jiffies;
 
        setup_timer_on_stack(&timer, process_timeout, (unsigned long)current);
-       __mod_timer(&timer, expire);
+       __mod_timer(&timer, expire, false);
        schedule();
        del_singleshot_timer_sync(&timer);