linux-kernel - [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying

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Date:   Thu,  6 Apr 2023 09:56:28 +0800
From:   Ye Bin <yebin@...weicloud.com>
To:     dennis@...nel.org, tj@...nel.org, cl@...ux.com, linux-mm@...ck.org,
        yury.norov@...il.com, andriy.shevchenko@...ux.intel.com,
        linux@...musvillemoes.dk
Cc:     linux-kernel@...r.kernel.org, dchinner@...hat.com,
        yebin10@...wei.com, yebin@...weicloud.com
Subject: [PATCH v2 1/2] cpu/hotplug: introduce 'num_dying_cpus' to get dying CPUs count

From: Ye Bin <yebin10@...wei.com>

Introduce '__num_dying_cpus' variable to cache the number of dying CPUs
in the core and just return the cached variable.

Signed-off-by: Ye Bin <yebin10@...wei.com>
---
 include/linux/cpumask.h | 20 ++++++++++++++++----
 kernel/cpu.c            |  2 ++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 2a61ddcf8321..8127fd598f51 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -135,6 +135,8 @@ extern struct cpumask __cpu_dying_mask;
 
 extern atomic_t __num_online_cpus;
 
+extern atomic_t __num_dying_cpus;
+
 extern cpumask_t cpus_booted_once_mask;
 
 static __always_inline void cpu_max_bits_warn(unsigned int cpu, unsigned int bits)
@@ -1018,10 +1020,14 @@ set_cpu_active(unsigned int cpu, bool active)
 static __always_inline void
 set_cpu_dying(unsigned int cpu, bool dying)
 {
-	if (dying)
-		cpumask_set_cpu(cpu, &__cpu_dying_mask);
-	else
-		cpumask_clear_cpu(cpu, &__cpu_dying_mask);
+	if (dying) {
+		if (!cpumask_test_and_set_cpu(cpu, &__cpu_dying_mask))
+			atomic_inc(&__num_dying_cpus);
+	}
+	else {
+		if (cpumask_test_and_clear_cpu(cpu, &__cpu_dying_mask))
+			atomic_dec(&__num_dying_cpus);
+	}
 }
 
 /**
@@ -1073,6 +1079,11 @@ static __always_inline unsigned int num_online_cpus(void)
 {
 	return arch_atomic_read(&__num_online_cpus);
 }
+
+static __always_inline unsigned int num_dying_cpus(void)
+{
+	return arch_atomic_read(&__num_dying_cpus);
+}
 #define num_possible_cpus()	cpumask_weight(cpu_possible_mask)
 #define num_present_cpus()	cpumask_weight(cpu_present_mask)
 #define num_active_cpus()	cpumask_weight(cpu_active_mask)
@@ -1108,6 +1119,7 @@ static __always_inline bool cpu_dying(unsigned int cpu)
 #define num_possible_cpus()	1U
 #define num_present_cpus()	1U
 #define num_active_cpus()	1U
+#define num_dying_cpus()	0U
 
 static __always_inline bool cpu_online(unsigned int cpu)
 {
diff --git a/kernel/cpu.c b/kernel/cpu.c
index f4a2c5845bcb..1c96c04cb259 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2662,6 +2662,8 @@ EXPORT_SYMBOL(__cpu_dying_mask);
 atomic_t __num_online_cpus __read_mostly;
 EXPORT_SYMBOL(__num_online_cpus);
 
+atomic_t __num_dying_cpus __read_mostly;
+
 void init_cpu_present(const struct cpumask *src)
 {
 	cpumask_copy(&__cpu_present_mask, src);
-- 
2.31.1