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Date:   Wed, 25 Oct 2023 18:03:22 +0000
From:   James Morse <>
Cc:     Fenghua Yu <>,
        Reinette Chatre <>,
        Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        H Peter Anvin <>,
        Babu Moger <>,
        James Morse <>,,
        D Scott Phillips OS <>,,,,,, Jamie Iles <>,
        Xin Hao <>,,,,
        Frederic Weisbecker <>
Subject: [PATCH v7 01/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef

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.

Tested-by: Shaopeng Tan <>
Tested-by: Peter Newman <>
Reviewed-by: Shaopeng Tan <>
Acked-by: Reinette Chatre <> # for resctrl dependency
CC: Frederic Weisbecker <>
Signed-off-by: James Morse <>
No changes since v6

 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 716d17f31c45..0fb903838dfb 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -164,9 +164,16 @@ 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 /* !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;
 extern bool tick_nohz_full_running;
-extern cpumask_var_t tick_nohz_full_mask;
 static inline bool tick_nohz_full_enabled(void)

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