[tip: x86/cache] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef

[tip-bot2 for James Morse]

The following commit has been merged into the x86/cache branch of tip:

Commit-ID:     31a5c0b7c674977889ce721d69101bc35f25e041
Gitweb:        https://git.kernel.org/tip/31a5c0b7c674977889ce721d69101bc35f25e041
Author:        James Morse <james.morse@xxxxxxx>
AuthorDate:    Tue, 13 Feb 2024 18:44:15 
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Fri, 16 Feb 2024 19:18:31 +01:00

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.

Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Reviewed-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Acked-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> # for resctrl dependency
Tested-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxx>
Tested-by: Peter Newman <peternewman@xxxxxxxxxx>
Tested-by: Carl Worth <carl@xxxxxxxxxxxxxxxxxxxxxx> # arm64
Link: https://lore.kernel.org/r/20240213184438.16675-2-james.morse@xxxxxxx
Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
---
 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 716d17f..0fb9038 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;
+
 #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)
 {