nohz: Separate idle sleeping time accounting from nohz logic

As we plan to be able to stop the tick outside the idle task, we
need to prepare for separating nohz logic from idle. As a start,
this pulls the idle sleeping time accounting out of the tick
stop/restart API to the callers on idle entry/exit.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
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@ti.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>

kernel/time/tick-sched.c

@@ -271,10 +271,10 @@ u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time)
 }
 EXPORT_SYMBOL_GPL(get_cpu_iowait_time_us);
 
-static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
+static void tick_nohz_stop_sched_tick(struct tick_sched *ts, ktime_t now)
 {
 	unsigned long seq, last_jiffies, next_jiffies, delta_jiffies;
-	ktime_t last_update, expires, now;
+	ktime_t last_update, expires;
 	struct clock_event_device *dev = __get_cpu_var(tick_cpu_device).evtdev;
 	u64 time_delta;
 	int cpu;
@@ -282,8 +282,6 @@ static void tick_nohz_stop_sched_tick(struct tick_sched *ts)
 	cpu = smp_processor_id();
 	ts = &per_cpu(tick_cpu_sched, cpu);
 
-	now = tick_nohz_start_idle(cpu, ts);
-
 	/*
 	 * If this cpu is offline and it is the one which updates
 	 * jiffies, then give up the assignment and let it be taken by
@@ -444,6 +442,14 @@ out:
 	ts->sleep_length = ktime_sub(dev->next_event, now);
 }
 
+static void __tick_nohz_idle_enter(struct tick_sched *ts)
+{
+	ktime_t now;
+
+	now = tick_nohz_start_idle(smp_processor_id(), ts);
+	tick_nohz_stop_sched_tick(ts, now);
+}
+
 /**
  * tick_nohz_idle_enter - stop the idle tick from the idle task
  *
@@ -479,7 +485,7 @@ void tick_nohz_idle_enter(void)
 	 * update of the idle time accounting in tick_nohz_start_idle().
 	 */
 	ts->inidle = 1;
-	tick_nohz_stop_sched_tick(ts);
+	__tick_nohz_idle_enter(ts);
 
 	local_irq_enable();
 }
@@ -499,7 +505,7 @@ void tick_nohz_irq_exit(void)
 	if (!ts->inidle)
 		return;
 
-	tick_nohz_stop_sched_tick(ts);
+	__tick_nohz_idle_enter(ts);
 }
 
 /**
@@ -540,39 +546,11 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now)
 	}
 }
 
-/**
- * tick_nohz_idle_exit - restart the idle tick from the idle task
- *
- * Restart the idle tick when the CPU is woken up from idle
- * This also exit the RCU extended quiescent state. The CPU
- * can use RCU again after this function is called.
- */
-void tick_nohz_idle_exit(void)
+static void tick_nohz_restart_sched_tick(struct tick_sched *ts, ktime_t now)
 {
-	int cpu = smp_processor_id();
-	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
 #ifndef CONFIG_VIRT_CPU_ACCOUNTING
 	unsigned long ticks;
 #endif
-	ktime_t now;
-
-	local_irq_disable();
-
-	WARN_ON_ONCE(!ts->inidle);
-
-	ts->inidle = 0;
-
-	if (ts->idle_active || ts->tick_stopped)
-		now = ktime_get();
-
-	if (ts->idle_active)
-		tick_nohz_stop_idle(cpu, now);
-
-	if (!ts->tick_stopped) {
-		local_irq_enable();
-		return;
-	}
-
 	/* Update jiffies first */
 	select_nohz_load_balancer(0);
 	tick_do_update_jiffies64(now);
@@ -600,6 +578,35 @@ void tick_nohz_idle_exit(void)
 	ts->idle_exittime = now;
 
 	tick_nohz_restart(ts, now);
+}
+
+/**
+ * tick_nohz_idle_exit - restart the idle tick from the idle task
+ *
+ * Restart the idle tick when the CPU is woken up from idle
+ * This also exit the RCU extended quiescent state. The CPU
+ * can use RCU again after this function is called.
+ */
+void tick_nohz_idle_exit(void)
+{
+	int cpu = smp_processor_id();
+	struct tick_sched *ts = &per_cpu(tick_cpu_sched, cpu);
+	ktime_t now;
+
+	local_irq_disable();
+
+	WARN_ON_ONCE(!ts->inidle);
+
+	ts->inidle = 0;
+
+	if (ts->idle_active || ts->tick_stopped)
+		now = ktime_get();
+
+	if (ts->idle_active)
+		tick_nohz_stop_idle(cpu, now);
+
+	if (ts->tick_stopped)
+		tick_nohz_restart_sched_tick(ts, now);
 
 	local_irq_enable();
 }