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Subject[PATCH 1/6] Expose do_timer CPU from tick-common
Date
This allows other parts of the kernel access to the tick_do_timer_cpu
variable in a controlled manner. The values will differ depending on
which mode is compiled in:

* CONFIG_HZ_PERIODIC: One (normally boot-cpu) is responsible for the
time update. This will never change unless the CPU is removed
(hotplugging). You will normally see a 0 returned every time here.

* CONFIG_NO_HZ_IDLE: system will disable periodic timer-interrupts on
the cpu if only the idle-task is running. This means that the timer
cpu will change often.

* CONFIG_NO_HZ_FULL: any CPU running only a single task can have
timer-interrupts disabled. As for NO_HZ_IDLE, timer CPU will change
often.

CC: Thomas Gleixner <tglx@linutronix.de>
CC: Peter Zijlstra <peterz@infradead.org>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: John Stultz <john.stultz@linaro.org>
Signed-off-by: Henrik Austad <haustad@cisco.com>
---
kernel/time/tick-common.c | 12 ++++++++++++
kernel/time/tick-internal.h | 1 +
2 files changed, 13 insertions(+)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index 20b2fe3..1729b4b 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -348,6 +348,18 @@ void tick_handover_do_timer(int *cpup)
}

/*
+ * Return the current timer-CPU (RO)
+ *
+ * Warning! this value can (and will) change depending on how timer-ticks are
+ * handled, the value returned could be outdated the moment it is read by
+ * userspace.
+ */
+int tick_expose_cpu(void)
+{
+ return tick_do_timer_cpu;
+}
+
+/*
* Shutdown an event device on a given cpu:
*
* This is called on a life CPU, when a CPU is dead. So we cannot
diff --git a/kernel/time/tick-internal.h b/kernel/time/tick-internal.h
index 8329669..5051dbd 100644
--- a/kernel/time/tick-internal.h
+++ b/kernel/time/tick-internal.h
@@ -154,5 +154,6 @@ static inline int tick_device_is_functional(struct clock_event_device *dev)

#endif

+extern int tick_expose_cpu(void);
extern void do_timer(unsigned long ticks);
extern void update_wall_time(void);
--
1.7.9.5


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