[PATCH v6 01/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef

[James Morse <james.morse@arm.com>]

tick_nohz_full_mask lists the CPUs that are nohz_full. This is only
needed when CONFIG_NO_HZ_FULL is defined. tick_nohz_full_cpu() allows
a specific CPU to be tested against the mask, and evaluates to false
when CONFIG_NO_HZ_FULL is not defined.

The resctrl code needs to pick a CPU to run some work on, a new helper
prefers housekeeping CPUs by examining the tick_nohz_full_mask. Hiding
the declaration behind #ifdef CONFIG_NO_HZ_FULL forces all the users to
be behind an ifdef too.

Move the tick_nohz_full_mask declaration, this lets callers drop the
ifdef, and guard access to tick_nohz_full_mask with IS_ENABLED() or
something like tick_nohz_full_cpu().

The definition does not need to be moved as any callers should be
removed at compile time unless CONFIG_NO_HZ_FULL is defined.

CC: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-By: Peter Newman <peternewman@google.com>
Signed-off-by: James Morse <james.morse@arm.com>
---
 include/linux/tick.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/tick.h b/include/linux/tick.h
index 9459fef5b857..65af90ca409a 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -174,9 +174,16 @@ static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
 static inline void tick_nohz_idle_stop_tick_protected(void) { }
 #endif /* !CONFIG_NO_HZ_COMMON */
 
+/*
+ * Mask of CPUs that are nohz_full.
+ *
+ * Users should be guarded by CONFIG_NO_HZ_FULL or a tick_nohz_full_cpu()
+ * check.
+ */
+extern cpumask_var_t tick_nohz_full_mask;
+
 #ifdef CONFIG_NO_HZ_FULL
 extern bool tick_nohz_full_running;
-extern cpumask_var_t tick_nohz_full_mask;
 
 static inline bool tick_nohz_full_enabled(void)
 {
-- 
2.39.2