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Message-Id: <20211218212014.1315894-14-yury.norov@gmail.com>
Date: Sat, 18 Dec 2021 13:20:09 -0800
From: Yury Norov <yury.norov@...il.com>
To: linux-kernel@...r.kernel.org, Yury Norov <yury.norov@...il.com>,
"James E.J. Bottomley" <jejb@...ux.ibm.com>,
"Martin K. Petersen" <martin.petersen@...cle.com>,
Michał Mirosław <mirq-linux@...e.qmqm.pl>,
"Paul E. McKenney" <paulmck@...nel.org>,
"Rafael J. Wysocki" <rafael@...nel.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Alexey Klimov <aklimov@...hat.com>,
Amitkumar Karwar <amitkarwar@...il.com>,
Andi Kleen <ak@...ux.intel.com>, Andrew Lunn <andrew@...n.ch>,
Andrew Morton <akpm@...ux-foundation.org>,
Andy Gross <agross@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Andy Shevchenko <andy@...radead.org>,
Anup Patel <anup.patel@....com>,
Ard Biesheuvel <ardb@...nel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
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Christoph Lameter <cl@...ux.com>,
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Subject: [PATCH 13/17] kernel/cpu: add num_possible_cpus counter
Similarly to the online cpus, the cpu_possible_mask is actively used
in the kernel. This patch adds a counter for possible cpus, so that
users that call num_possible_cpus() would know the result immediately,
instead of calling the bitmap_weight for the mask underlying.
Suggested-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
include/linux/cpumask.h | 30 ++++++++++++++++--------------
kernel/cpu.c | 22 ++++++++++++++++++++++
2 files changed, 38 insertions(+), 14 deletions(-)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 1906e3225737..0be2504d8e4c 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -99,6 +99,7 @@ extern struct cpumask __cpu_dying_mask;
#define cpu_dying_mask ((const struct cpumask *)&__cpu_dying_mask)
extern atomic_t __num_online_cpus;
+extern atomic_t __num_possible_cpus;
extern cpumask_t cpus_booted_once_mask;
@@ -870,19 +871,8 @@ void init_cpu_present(const struct cpumask *src);
void init_cpu_possible(const struct cpumask *src);
void init_cpu_online(const struct cpumask *src);
-static inline void reset_cpu_possible_mask(void)
-{
- bitmap_zero(cpumask_bits(&__cpu_possible_mask), NR_CPUS);
-}
-
-static inline void
-set_cpu_possible(unsigned int cpu, bool possible)
-{
- if (possible)
- cpumask_set_cpu(cpu, &__cpu_possible_mask);
- else
- cpumask_clear_cpu(cpu, &__cpu_possible_mask);
-}
+void set_cpu_possible(unsigned int cpu, bool possible);
+void reset_cpu_possible_mask(void);
static inline void
set_cpu_present(unsigned int cpu, bool present)
@@ -962,7 +952,19 @@ static inline unsigned int num_online_cpus(void)
{
return atomic_read(&__num_online_cpus);
}
-#define num_possible_cpus() cpumask_weight(cpu_possible_mask)
+
+/**
+ * num_possible_cpus() - Read the number of possible CPUs
+ *
+ * Despite the fact that __num_possible_cpus is of type atomic_t, this
+ * interface gives only a momentary snapshot and is not protected against
+ * concurrent CPU hotplug operations unless invoked from a cpuhp_lock held
+ * region.
+ */
+static inline unsigned int num_possible_cpus(void)
+{
+ return atomic_read(&__num_possible_cpus);
+}
#define num_present_cpus() cpumask_weight(cpu_present_mask)
#define num_active_cpus() cpumask_weight(cpu_active_mask)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index cd7605204d4d..a0a815911173 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2583,10 +2583,13 @@ EXPORT_SYMBOL(cpu_all_bits);
#ifdef CONFIG_INIT_ALL_POSSIBLE
struct cpumask __cpu_possible_mask __read_mostly
= {CPU_BITS_ALL};
+atomic_t __num_possible_cpus __read_mostly = ATOMIC_INIT(NR_CPUS);
#else
struct cpumask __cpu_possible_mask __read_mostly;
+atomic_t __num_possible_cpus __read_mostly;
#endif
EXPORT_SYMBOL(__cpu_possible_mask);
+EXPORT_SYMBOL(__num_possible_cpus);
struct cpumask __cpu_online_mask __read_mostly;
EXPORT_SYMBOL(__cpu_online_mask);
@@ -2611,6 +2614,7 @@ void init_cpu_present(const struct cpumask *src)
void init_cpu_possible(const struct cpumask *src)
{
cpumask_copy(&__cpu_possible_mask, src);
+ atomic_set(&__num_possible_cpus, cpumask_weight(cpu_possible_mask));
}
void init_cpu_online(const struct cpumask *src)
@@ -2640,6 +2644,24 @@ void set_cpu_online(unsigned int cpu, bool online)
}
}
+void reset_cpu_possible_mask(void)
+{
+ bitmap_zero(cpumask_bits(&__cpu_possible_mask), NR_CPUS);
+ atomic_set(&__num_possible_cpus, 0);
+}
+
+void set_cpu_possible(unsigned int cpu, bool possible)
+{
+ if (possible) {
+ if (!cpumask_test_and_set_cpu(cpu, &__cpu_possible_mask))
+ atomic_inc(&__num_possible_cpus);
+ } else {
+ if (cpumask_test_and_clear_cpu(cpu, &__cpu_possible_mask))
+ atomic_dec(&__num_possible_cpus);
+ }
+}
+EXPORT_SYMBOL(set_cpu_possible);
+
/*
* Activate the first processor.
*/
--
2.30.2
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