nohz: Wake up full dynticks CPUs when a timer gets enqueued

Wake up a CPU when a timer list timer is enqueued there and
the target is part of the full dynticks range. Sending an IPI
to it makes it reconsidering the next timer to program on top
of recent updates.

This may later be improved by checking if the tick is really
stopped on the target. This would need some careful
synchronization though. So deal with such optimization later
and start simple.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 9004f6e19eacc462ba719e6bc9a4639bdea16928..10626e2ee688f40247806544beb9a9f273a78336 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1851,9 +1851,9 @@ static inline void idle_task_exit(void) {}
 #endif
 
 #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
-extern void wake_up_idle_cpu(int cpu);
+extern void wake_up_nohz_cpu(int cpu);
 #else
-static inline void wake_up_idle_cpu(int cpu) { }
+static inline void wake_up_nohz_cpu(int cpu) { }
 #endif
 
 #ifdef CONFIG_SCHED_AUTOGROUP

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 849deb96e61ed127e79f5aec83d7cd60002da048..e91ee589f7936bd8338c1c79d99b1c5fca285060 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -587,7 +587,7 @@ unlock:
  * account when the CPU goes back to idle and evaluates the timer
  * wheel for the next timer event.
  */
-void wake_up_idle_cpu(int cpu)
+static void wake_up_idle_cpu(int cpu)
 {
        struct rq *rq = cpu_rq(cpu);
 
@@ -617,6 +617,24 @@ void wake_up_idle_cpu(int cpu)
                smp_send_reschedule(cpu);
 }
 
+static bool wake_up_extended_nohz_cpu(int cpu)
+{
+       if (tick_nohz_extended_cpu(cpu)) {
+               if (cpu != smp_processor_id() ||
+                   tick_nohz_tick_stopped())
+                       smp_send_reschedule(cpu);
+               return true;
+       }
+
+       return false;
+}
+
+void wake_up_nohz_cpu(int cpu)
+{
+       if (!wake_up_extended_nohz_cpu(cpu))
+               wake_up_idle_cpu(cpu);
+}
+
 static inline bool got_nohz_idle_kick(void)
 {
        int cpu = smp_processor_id();

diff --git a/kernel/timer.c b/kernel/timer.c
index dbf7a78a1ef14a0200a1a28835ebb292be2aae4c..4e3040b40d162834e471fe1a1cb8faa6558b8e32 100644 (file)
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -930,14 +930,14 @@ void add_timer_on(struct timer_list *timer, int cpu)
        debug_activate(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
+        * Check whether the other CPU is in dynticks mode and needs
+        * to be triggered to reevaluate the timer wheel.
+        * 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.
+        * makes sure that a CPU on the way to stop its tick can not
+        * evaluate the timer wheel.
         */
-       wake_up_idle_cpu(cpu);
+       wake_up_nohz_cpu(cpu);
        spin_unlock_irqrestore(&base->lock, flags);
 }
 EXPORT_SYMBOL_GPL(add_timer_on);