nohz: Implement full dynticks kick

Implement the full dynticks kick that is performed from
IPIs sent by various subsystems (scheduler, posix timers, ...)
when they want to notify about a new event that may
reconsider the dependency on the tick.

Most of the time, such an event end up restarting the tick.

(Part of the design with subsystems providing *_can_stop_tick()
helpers suggested by Peter Zijlstra a while ago).

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
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: Oleg Nesterov <oleg@redhat.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>

1 files changed, 38 insertions, 4 deletions

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 4d74a68b2c34..95d79aeb3e27 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -21,6 +21,8 @@
 #include <linux/sched.h>
 #include <linux/module.h>
 #include <linux/irq_work.h>
+#include <linux/posix-timers.h>
+#include <linux/perf_event.h>
 
 #include <asm/irq_regs.h>
 
@@ -147,16 +149,48 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs)
 static cpumask_var_t nohz_full_mask;
 bool have_nohz_full_mask;
 
+static bool can_stop_full_tick(void)
+{
+        WARN_ON_ONCE(!irqs_disabled());
+
+        if (!sched_can_stop_tick())
+                return false;
+
+        if (!posix_cpu_timers_can_stop_tick(current))
+                return false;
+
+        if (!perf_event_can_stop_tick())
+                return false;
+
+        /* sched_clock_tick() needs us? */
+#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
+        /*
+         * TODO: kick full dynticks CPUs when
+         * sched_clock_stable is set.
+         */
+        if (!sched_clock_stable)
+                return false;
+#endif
+
+        return true;
+}
+
+static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now);
+
 /*
  * Re-evaluate the need for the tick on the current CPU
  * and restart it if necessary.
  */
 void tick_nohz_full_check(void)
 {
-        /*
-         * STUB for now, will be filled with the full tick stop/restart
-         * infrastructure patches
-         */
+        struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+        if (tick_nohz_full_cpu(smp_processor_id())) {
+                if (ts->tick_stopped && !is_idle_task(current)) {
+                        if (!can_stop_full_tick())
+                                tick_nohz_restart_sched_tick(ts, ktime_get());
+                }
+        }
 }
 
 static void nohz_full_kick_work_func(struct irq_work *work)