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[216.228.112.21]) by smtp.gmail.com with ESMTPSA id e21sm2358431ote.72.2021.12.18.13.20.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 18 Dec 2021 13:20:58 -0800 (PST) From: Yury Norov To: linux-kernel@vger.kernel.org, Yury Norov , "James E.J. Bottomley" , "Martin K. Petersen" , =?utf-8?b?TWljaGHFgiBN?= =?utf-8?b?aXJvc8WCYXc=?= , "Paul E. McKenney" , "Rafael J. Wysocki" , Alexander Shishkin , Alexey Klimov , Amitkumar Karwar , Andi Kleen , Andrew Lunn , Andrew Morton , Andy Gross , Andy Lutomirski , Andy Shevchenko , Anup Patel , Ard Biesheuvel , Arnaldo Carvalho de Melo , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christoph Hellwig , Christoph Lameter , Daniel Vetter , Dave Hansen , David Airlie , David Laight , Dennis Zhou , Emil Renner Berthing , Geert Uytterhoeven , Geetha sowjanya , Greg Kroah-Hartman , Guo Ren , Hans de Goede , Heiko Carstens , Ian Rogers , Ingo Molnar , Jakub Kicinski , Jason Wessel , Jens Axboe , Jiri Olsa , Joe Perches , Jonathan Cameron , Juri Lelli , Kees Cook , Krzysztof Kozlowski , Lee Jones , Marc Zyngier , Marcin Wojtas , Mark Gross , Mark Rutland , Matti Vaittinen , Mauro Carvalho Chehab , Mel Gorman , Michael Ellerman , Mike Marciniszyn , Nicholas Piggin , Palmer Dabbelt , Peter Zijlstra , Petr Mladek , Randy Dunlap , Rasmus Villemoes , Russell King , Saeed Mahameed , Sagi Grimberg , Sergey Senozhatsky , Solomon Peachy , Stephen Boyd , Stephen Rothwell , Steven Rostedt , Subbaraya Sundeep , Sudeep Holla , Sunil Goutham , Tariq Toukan , Tejun Heo , Thomas Bogendoerfer , Thomas Gleixner , Ulf Hansson , Vincent Guittot , Vineet Gupta , Viresh Kumar , Vivien Didelot , Vlastimil Babka , Will Deacon , bcm-kernel-feedback-list@broadcom.com, kvm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-csky@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Subject: [PATCH 13/17] kernel/cpu: add num_possible_cpus counter Date: Sat, 18 Dec 2021 13:20:09 -0800 Message-Id: <20211218212014.1315894-14-yury.norov@gmail.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20211218212014.1315894-1-yury.norov@gmail.com> References: <20211218212014.1315894-1-yury.norov@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org 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 Signed-off-by: Yury Norov --- 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. */