nohz: Rename CONFIG_NO_HZ to CONFIG_NO_HZ_COMMON

We are planning to convert the dynticks Kconfig options layout
into a choice menu. The user must be able to easily pick
any of the following implementations: constant periodic tick,
idle dynticks, full dynticks.

As this implies a mutual exclusion, the two dynticks implementions
need to converge on the selection of a common Kconfig option in order
to ease the sharing of a common infrastructure.

It would thus seem pretty natural to reuse CONFIG_NO_HZ to
that end. It already implements all the idle dynticks code
and the full dynticks depends on all that code for now.
So ideally the choice menu would propose CONFIG_NO_HZ_IDLE and
CONFIG_NO_HZ_EXTENDED then both would select CONFIG_NO_HZ.

On the other hand we want to stay backward compatible: if
CONFIG_NO_HZ is set in an older config file, we want to
enable CONFIG_NO_HZ_IDLE by default.

But we can't afford both at the same time or we run into
a circular dependency:

1) CONFIG_NO_HZ_IDLE and CONFIG_NO_HZ_EXTENDED both select
   CONFIG_NO_HZ
2) If CONFIG_NO_HZ is set, we default to CONFIG_NO_HZ_IDLE

We might be able to support that from Kconfig/Kbuild but it
may not be wise to introduce such a confusing behaviour.

So to solve this, create a new CONFIG_NO_HZ_COMMON option
which gathers the common code between idle and full dynticks
(that common code for now is simply the idle dynticks code)
and select it from their referring Kconfig.

Then we'll later create CONFIG_NO_HZ_IDLE and map CONFIG_NO_HZ
to it for backward compatibility.

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>

1 files changed, 4 insertions, 4 deletions

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 44bfa8aa439f..5e403339ee14 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -82,7 +82,7 @@ extern int tick_program_event(ktime_t expires, int force);
 extern void tick_setup_sched_timer(void);
 # endif
 
-# if defined CONFIG_NO_HZ || defined CONFIG_HIGH_RES_TIMERS
+# if defined CONFIG_NO_HZ_COMMON || defined CONFIG_HIGH_RES_TIMERS
 extern void tick_cancel_sched_timer(int cpu);
 # else
 static inline void tick_cancel_sched_timer(int cpu) { }
@@ -123,7 +123,7 @@ static inline void tick_check_idle(int cpu) { }
 static inline int tick_oneshot_mode_active(void) { return 0; }
 #endif /* !CONFIG_GENERIC_CLOCKEVENTS */
 
-# ifdef CONFIG_NO_HZ
+# ifdef CONFIG_NO_HZ_COMMON
 DECLARE_PER_CPU(struct tick_sched, tick_cpu_sched);
 
 static inline int tick_nohz_tick_stopped(void)
@@ -138,7 +138,7 @@ extern ktime_t tick_nohz_get_sleep_length(void);
 extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
 extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
 
-# else /* !CONFIG_NO_HZ */
+# else /* !CONFIG_NO_HZ_COMMON */
 static inline int tick_nohz_tick_stopped(void)
 {
 	return 0;
@@ -155,7 +155,7 @@ static inline ktime_t tick_nohz_get_sleep_length(void)
 }
 static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
 static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
-# endif /* !NO_HZ */
+# endif /* !CONFIG_NO_HZ_COMMON */
 
 #ifdef CONFIG_NO_HZ_EXTENDED
 extern int tick_nohz_extended_cpu(int cpu);