1 files changed, 98 insertions, 39 deletions

diff --git a/kernel/timer.c b/kernel/timer.c
index aeb6a54f2771..9199f3c52215 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -319,6 +319,24 @@ unsigned long round_jiffies_up_relative(unsigned long j)
 }
 EXPORT_SYMBOL_GPL(round_jiffies_up_relative);
 
+/**
+ * set_timer_slack - set the allowed slack for a timer
+ * @slack_hz: the amount of time (in jiffies) allowed for rounding
+ *
+ * Set the amount of time, in jiffies, that a certain timer has
+ * in terms of slack. By setting this value, the timer subsystem
+ * will schedule the actual timer somewhere between
+ * the time mod_timer() asks for, and that time plus the slack.
+ *
+ * By setting the slack to -1, a percentage of the delay is used
+ * instead.
+ */
+void set_timer_slack(struct timer_list *timer, int slack_hz)
+{
+        timer->slack = slack_hz;
+}
+EXPORT_SYMBOL_GPL(set_timer_slack);
+
 
 static inline void set_running_timer(struct tvec_base *base,
                                         struct timer_list *timer)
@@ -550,6 +568,7 @@ static void __init_timer(struct timer_list *timer,
 {
         timer->entry.next = NULL;
         timer->base = __raw_get_cpu_var(tvec_bases);
+        timer->slack = -1;
 #ifdef CONFIG_TIMER_STATS
         timer->start_site = NULL;
         timer->start_pid = -1;
@@ -715,6 +734,41 @@ int mod_timer_pending(struct timer_list *timer, unsigned long expires)
 }
 EXPORT_SYMBOL(mod_timer_pending);
 
+/*
+ * Decide where to put the timer while taking the slack into account
+ *
+ * Algorithm:
+ *   1) calculate the maximum (absolute) time
+ *   2) calculate the highest bit where the expires and new max are different
+ *   3) use this bit to make a mask
+ *   4) use the bitmask to round down the maximum time, so that all last
+ *      bits are zeros
+ */
+static inline
+unsigned long apply_slack(struct timer_list *timer, unsigned long expires)
+{
+        unsigned long expires_limit, mask;
+        int bit;
+
+        expires_limit = expires + timer->slack;
+
+        if (timer->slack < 0) /* auto slack: use 0.4% */
+                expires_limit = expires + (expires - jiffies)/256;
+
+        mask = expires ^ expires_limit;
+
+        if (mask == 0)
+                return expires;
+
+        bit = find_last_bit(&mask, BITS_PER_LONG);
+
+        mask = (1 << bit) - 1;
+
+        expires_limit = expires_limit & ~(mask);
+
+        return expires_limit;
+}
+
 /**
  * mod_timer - modify a timer's timeout
  * @timer: the timer to be modified
@@ -745,6 +799,8 @@ int mod_timer(struct timer_list *timer, unsigned long expires)
         if (timer_pending(timer) && timer->expires == expires)
                 return 1;
 
+        expires = apply_slack(timer, expires);
+
         return __mod_timer(timer, expires, false, TIMER_NOT_PINNED);
 }
 EXPORT_SYMBOL(mod_timer);
@@ -955,6 +1011,47 @@ static int cascade(struct tvec_base *base, struct tvec *tv, int index)
         return index;
 }
 
+static void call_timer_fn(struct timer_list *timer, void (*fn)(unsigned long),
+                          unsigned long data)
+{
+        int preempt_count = preempt_count();
+
+#ifdef CONFIG_LOCKDEP
+        /*
+         * It is permissible to free the timer from inside the
+         * function that is called from it, this we need to take into
+         * account for lockdep too. To avoid bogus "held lock freed"
+         * warnings as well as problems when looking into
+         * timer->lockdep_map, make a copy and use that here.
+         */
+        struct lockdep_map lockdep_map = timer->lockdep_map;
+#endif
+        /*
+         * Couple the lock chain with the lock chain at
+         * del_timer_sync() by acquiring the lock_map around the fn()
+         * call here and in del_timer_sync().
+         */
+        lock_map_acquire(&lockdep_map);
+
+        trace_timer_expire_entry(timer);
+        fn(data);
+        trace_timer_expire_exit(timer);
+
+        lock_map_release(&lockdep_map);
+
+        if (preempt_count != preempt_count()) {
+                WARN_ONCE(1, "timer: %pF preempt leak: %08x -> %08x\n",
+                          fn, preempt_count, preempt_count());
+                /*
+                 * Restore the preempt count. That gives us a decent
+                 * chance to survive and extract information. If the
+                 * callback kept a lock held, bad luck, but not worse
+                 * than the BUG() we had.
+                 */
+                preempt_count() = preempt_count;
+        }
+}
+
 #define INDEX(N) ((base->timer_jiffies >> (TVR_BITS + (N) * TVN_BITS)) & TVN_MASK)
 
 /**
@@ -998,45 +1095,7 @@ static inline void __run_timers(struct tvec_base *base)
                         detach_timer(timer, 1);
 
                         spin_unlock_irq(&base->lock);
-                        {
-                                int preempt_count = preempt_count();
-
-#ifdef CONFIG_LOCKDEP
-                                /*
-                                 * It is permissible to free the timer from
-                                 * inside the function that is called from
-                                 * it, this we need to take into account for
-                                 * lockdep too. To avoid bogus "held lock
-                                 * freed" warnings as well as problems when
-                                 * looking into timer->lockdep_map, make a
-                                 * copy and use that here.
-                                 */
-                                struct lockdep_map lockdep_map =
-                                        timer->lockdep_map;
-#endif
-                                /*
-                                 * Couple the lock chain with the lock chain at
-                                 * del_timer_sync() by acquiring the lock_map
-                                 * around the fn() call here and in
-                                 * del_timer_sync().
-                                 */
-                                lock_map_acquire(&lockdep_map);
-
-                                trace_timer_expire_entry(timer);
-                                fn(data);
-                                trace_timer_expire_exit(timer);
-
-                                lock_map_release(&lockdep_map);
-
-                                if (preempt_count != preempt_count()) {
-                                        printk(KERN_ERR "huh, entered %p "
-                                               "with preempt_count %08x, exited"
-                                               " with %08x?\n",
-                                               fn, preempt_count,
-                                               preempt_count());
-                                        BUG();
-                                }
-                        }
+                        call_timer_fn(timer, fn, data);
                         spin_lock_irq(&base->lock);
                 }
         }