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From: James Morse <james.morse@arm.com>
To: x86@kernel.org,
	linux-kernel@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>,
	Reinette Chatre <reinette.chatre@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	H Peter Anvin <hpa@zytor.com>,
	Babu Moger <Babu.Moger@amd.com>,
	James Morse <james.morse@arm.com>,
	shameerali.kolothum.thodi@huawei.com,
	D Scott Phillips OS <scott@os.amperecomputing.com>,
	carl@os.amperecomputing.com,
	lcherian@marvell.com,
	bobo.shaobowang@huawei.com,
	tan.shaopeng@fujitsu.com,
	baolin.wang@linux.alibaba.com,
	Jamie Iles <quic_jiles@quicinc.com>,
	Xin Hao <xhao@linux.alibaba.com>,
	peternewman@google.com,
	dfustini@baylibre.com,
	amitsinght@marvell.com,
	Frederic Weisbecker <frederic@kernel.org>
Subject: [PATCH v8 01/24] tick/nohz: Move tick_nohz_full_mask declaration outside the #ifdef
Date: Fri, 15 Dec 2023 17:43:20 +0000
Message-Id: <20231215174343.13872-2-james.morse@arm.com>
In-Reply-To: <20231215174343.13872-1-james.morse@arm.com>
References: <20231215174343.13872-1-james.morse@arm.com>
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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@arm.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Peter Newman <peternewman@google.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Acked-by: Reinette Chatre <reinette.chatre@intel.com> # for resctrl dependency
CC: Frederic Weisbecker <frederic@kernel.org>
---
 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;
+
 #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)
 {
-- 
2.20.1