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Subject[RFC/RFT][PATCH 1/7] time: tick-sched: Reorganize idle tick management code
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Prepare two pieces of code in tick_nohz_idle_enter() for being
called separately from each other.

First, make it possible to call the initial preparatory part of
tick_nohz_idle_enter() without the tick-stopping part following
it and introduce the tick_nohz_idle_prepare() wrapper for that
(that will be used in the next set of changes).

Second, add a new stop_tick argument to __tick_nohz_idle_enter()
tell it whether or not to stop the tick (that is always set for
now) and add a wrapper allowing this function to be called from
the outside of tick-sched.c.

Just the code reorganization and two new wrapper functions, no
intended functional changes.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
include/linux/tick.h | 2 +
kernel/time/tick-sched.c | 51 +++++++++++++++++++++++++++++++----------------
2 files changed, 36 insertions(+), 17 deletions(-)

Index: linux-pm/include/linux/tick.h
===================================================================
--- linux-pm.orig/include/linux/tick.h
+++ linux-pm/include/linux/tick.h
@@ -114,6 +114,8 @@ enum tick_dep_bits {
#ifdef CONFIG_NO_HZ_COMMON
extern bool tick_nohz_enabled;
extern int tick_nohz_tick_stopped(void);
+extern void tick_nohz_idle_prepare(void);
+extern void tick_nohz_idle_go_idle(bool stop_tick);
extern void tick_nohz_idle_enter(void);
extern void tick_nohz_idle_exit(void);
extern void tick_nohz_irq_exit(void);
Index: linux-pm/kernel/time/tick-sched.c
===================================================================
--- linux-pm.orig/kernel/time/tick-sched.c
+++ linux-pm/kernel/time/tick-sched.c
@@ -911,14 +911,14 @@ static bool can_stop_idle_tick(int cpu,
return true;
}

-static void __tick_nohz_idle_enter(struct tick_sched *ts)
+static void __tick_nohz_idle_enter(struct tick_sched *ts, bool stop_tick)
{
ktime_t now, expires;
int cpu = smp_processor_id();

now = tick_nohz_start_idle(ts);

- if (can_stop_idle_tick(cpu, ts)) {
+ if (can_stop_idle_tick(cpu, ts) && stop_tick) {
int was_stopped = ts->tick_stopped;

ts->idle_calls++;
@@ -936,19 +936,7 @@ static void __tick_nohz_idle_enter(struc
}
}

-/**
- * tick_nohz_idle_enter - stop the idle tick from the idle task
- *
- * When the next event is more than a tick into the future, stop the idle tick
- * Called when we start the idle loop.
- *
- * The arch is responsible of calling:
- *
- * - rcu_idle_enter() after its last use of RCU before the CPU is put
- * to sleep.
- * - rcu_idle_exit() before the first use of RCU after the CPU is woken up.
- */
-void tick_nohz_idle_enter(void)
+void __tick_nohz_idle_prepare(void)
{
struct tick_sched *ts;

@@ -965,7 +953,36 @@ void tick_nohz_idle_enter(void)

ts = this_cpu_ptr(&tick_cpu_sched);
ts->inidle = 1;
- __tick_nohz_idle_enter(ts);
+}
+
+/**
+ * tick_nohz_idle_prepare - prepare for entering idle on the current CPU.
+ *
+ * Called when we start the idle loop.
+ */
+void tick_nohz_idle_prepare(void)
+{
+ __tick_nohz_idle_prepare();
+
+ local_irq_enable();
+}
+
+/**
+ * tick_nohz_idle_go_idle - start idle period on the current CPU.
+ * @stop_tick: Whether or not to stop the idle tick.
+ *
+ * When @stop_tick is set and the next event is more than a tick into the
+ * future, stop the idle tick.
+ */
+void tick_nohz_idle_go_idle(bool stop_tick)
+{
+ __tick_nohz_idle_enter(this_cpu_ptr(&tick_cpu_sched), stop_tick);
+}
+
+void tick_nohz_idle_enter(void)
+{
+ __tick_nohz_idle_prepare();
+ tick_nohz_idle_go_idle(true);

local_irq_enable();
}
@@ -983,7 +1000,7 @@ void tick_nohz_irq_exit(void)
struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);

if (ts->inidle)
- __tick_nohz_idle_enter(ts);
+ __tick_nohz_idle_enter(ts, true);
else
tick_nohz_full_update_tick(ts);
}
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