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Message-Id: <20211218212014.1315894-16-yury.norov@gmail.com>
Date: Sat, 18 Dec 2021 13:20:11 -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>,
Catalin Marinas <catalin.marinas@....com>,
Christoph Hellwig <hch@....de>,
Christoph Lameter <cl@...ux.com>,
Daniel Vetter <daniel@...ll.ch>,
Dave Hansen <dave.hansen@...ux.intel.com>,
David Airlie <airlied@...ux.ie>,
David Laight <David.Laight@...LAB.COM>,
Dennis Zhou <dennis@...nel.org>,
Emil Renner Berthing <kernel@...il.dk>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Geetha sowjanya <gakula@...vell.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Guo Ren <guoren@...nel.org>,
Hans de Goede <hdegoede@...hat.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Ian Rogers <irogers@...gle.com>,
Ingo Molnar <mingo@...hat.com>,
Jakub Kicinski <kuba@...nel.org>,
Jason Wessel <jason.wessel@...driver.com>,
Jens Axboe <axboe@...com>, Jiri Olsa <jolsa@...hat.com>,
Joe Perches <joe@...ches.com>,
Jonathan Cameron <jic23@...nel.org>,
Juri Lelli <juri.lelli@...hat.com>,
Kees Cook <keescook@...omium.org>,
Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
Lee Jones <lee.jones@...aro.org>,
Marc Zyngier <maz@...nel.org>, Marcin Wojtas <mw@...ihalf.com>,
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Mel Gorman <mgorman@...e.de>,
Michael Ellerman <mpe@...erman.id.au>,
Mike Marciniszyn <mike.marciniszyn@...nelisnetworks.com>,
Nicholas Piggin <npiggin@...il.com>,
Palmer Dabbelt <palmer@...belt.com>,
Peter Zijlstra <peterz@...radead.org>,
Petr Mladek <pmladek@...e.com>,
Randy Dunlap <rdunlap@...radead.org>,
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Thomas Gleixner <tglx@...utronix.de>,
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Viresh Kumar <viresh.kumar@...aro.org>,
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Vlastimil Babka <vbabka@...e.cz>,
Will Deacon <will@...nel.org>,
bcm-kernel-feedback-list@...adcom.com, kvm@...r.kernel.org,
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Subject: [PATCH 15/17] kernel/cpu: add num_active_cpu counter
Similarly to the online cpus, the cpu_active_mask is actively used
in the kernel. This patch adds a counter for active cpus, so that
users that call num_active_cpus() would know the result immediately,
instead of calling the bitmap_weight for the mask.
Suggested-by: Nicholas Piggin <npiggin@...il.com>
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
include/linux/cpumask.h | 26 +++++++++++++++-----------
kernel/cpu.c | 15 +++++++++++++++
2 files changed, 30 insertions(+), 11 deletions(-)
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index c2a9d15e2cbd..0add872898f8 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -101,6 +101,7 @@ extern struct cpumask __cpu_dying_mask;
extern atomic_t __num_online_cpus;
extern atomic_t __num_possible_cpus;
extern atomic_t __num_present_cpus;
+extern atomic_t __num_active_cpus;
extern cpumask_t cpus_booted_once_mask;
@@ -875,17 +876,8 @@ void init_cpu_online(const struct cpumask *src);
void set_cpu_possible(unsigned int cpu, bool possible);
void reset_cpu_possible_mask(void);
void set_cpu_present(unsigned int cpu, bool present);
-
void set_cpu_online(unsigned int cpu, bool online);
-
-static inline void
-set_cpu_active(unsigned int cpu, bool active)
-{
- if (active)
- cpumask_set_cpu(cpu, &__cpu_active_mask);
- else
- cpumask_clear_cpu(cpu, &__cpu_active_mask);
-}
+void set_cpu_active(unsigned int cpu, bool active);
static inline void
set_cpu_dying(unsigned int cpu, bool dying)
@@ -971,7 +963,19 @@ static inline unsigned int num_present_cpus(void)
{
return atomic_read(&__num_present_cpus);
}
-#define num_active_cpus() cpumask_weight(cpu_active_mask)
+
+/**
+ * num_active_cpus() - Read the number of active CPUs
+ *
+ * Despite the fact that __num_active_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_active_cpus(void)
+{
+ return atomic_read(&__num_active_cpus);
+}
static inline bool cpu_online(unsigned int cpu)
{
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 1f7ea1bdde1a..62b411d88810 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -2603,6 +2603,9 @@ EXPORT_SYMBOL(__num_present_cpus);
struct cpumask __cpu_active_mask __read_mostly;
EXPORT_SYMBOL(__cpu_active_mask);
+atomic_t __num_active_cpus __read_mostly;
+EXPORT_SYMBOL(__num_active_cpus);
+
struct cpumask __cpu_dying_mask __read_mostly;
EXPORT_SYMBOL(__cpu_dying_mask);
@@ -2678,6 +2681,18 @@ void set_cpu_present(unsigned int cpu, bool present)
}
EXPORT_SYMBOL(set_cpu_present);
+void set_cpu_active(unsigned int cpu, bool active)
+{
+ if (active) {
+ if (!cpumask_test_and_set_cpu(cpu, &__cpu_active_mask))
+ atomic_inc(&__num_active_cpus);
+ } else {
+ if (cpumask_test_and_clear_cpu(cpu, &__cpu_active_mask))
+ atomic_dec(&__num_active_cpus);
+ }
+}
+EXPORT_SYMBOL(set_cpu_active);
+
/*
* Activate the first processor.
*/
--
2.30.2
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