From 35a5c37cb9f1f947dff18e7cfc75a8cfcfd557ca Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 19 Nov 2025 18:27:01 +0100 Subject: [PATCH] cpumask: Cache num_possible_cpus() Reevaluating num_possible_cpus() over and over does not make sense. That becomes a constant after init as cpu_possible_mask is marked ro_after_init. Cache the value during initialization and provide that for consumption. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Thomas Gleixner Reviewed-by: Yury Norov Reviewed-by: Mathieu Desnoyers Reviewed-by: Shrikanth Hegde Link: https://patch.msgid.link/20251119172549.578653738@linutronix.de --- include/linux/cpumask.h | 10 ++++++++-- kernel/cpu.c | 19 +++++++++++++++++++ 2 files changed, 27 insertions(+), 2 deletions(-) diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h index feba06eb0a42e..66694ee8d86e9 100644 --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -126,6 +126,7 @@ extern struct cpumask __cpu_dying_mask; #define cpu_dying_mask ((const struct cpumask *)&__cpu_dying_mask) extern atomic_t __num_online_cpus; +extern unsigned int __num_possible_cpus; extern cpumask_t cpus_booted_once_mask; @@ -1152,13 +1153,13 @@ void init_cpu_possible(const struct cpumask *src); #define __assign_cpu(cpu, mask, val) \ __assign_bit(cpumask_check(cpu), cpumask_bits(mask), (val)) -#define set_cpu_possible(cpu, possible) assign_cpu((cpu), &__cpu_possible_mask, (possible)) #define set_cpu_enabled(cpu, enabled) assign_cpu((cpu), &__cpu_enabled_mask, (enabled)) #define set_cpu_present(cpu, present) assign_cpu((cpu), &__cpu_present_mask, (present)) #define set_cpu_active(cpu, active) assign_cpu((cpu), &__cpu_active_mask, (active)) #define set_cpu_dying(cpu, dying) assign_cpu((cpu), &__cpu_dying_mask, (dying)) void set_cpu_online(unsigned int cpu, bool online); +void set_cpu_possible(unsigned int cpu, bool possible); /** * to_cpumask - convert a NR_CPUS bitmap to a struct cpumask * @@ -1211,7 +1212,12 @@ static __always_inline unsigned int num_online_cpus(void) { return raw_atomic_read(&__num_online_cpus); } -#define num_possible_cpus() cpumask_weight(cpu_possible_mask) + +static __always_inline unsigned int num_possible_cpus(void) +{ + return __num_possible_cpus; +} + #define num_enabled_cpus() cpumask_weight(cpu_enabled_mask) #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 db9f6c539b28c..b674fdf96208b 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -3085,10 +3085,13 @@ EXPORT_SYMBOL(cpu_all_bits); #ifdef CONFIG_INIT_ALL_POSSIBLE struct cpumask __cpu_possible_mask __ro_after_init = {CPU_BITS_ALL}; +unsigned int __num_possible_cpus __ro_after_init = NR_CPUS; #else struct cpumask __cpu_possible_mask __ro_after_init; +unsigned int __num_possible_cpus __ro_after_init; #endif EXPORT_SYMBOL(__cpu_possible_mask); +EXPORT_SYMBOL(__num_possible_cpus); struct cpumask __cpu_online_mask __read_mostly; EXPORT_SYMBOL(__cpu_online_mask); @@ -3116,6 +3119,7 @@ void init_cpu_present(const struct cpumask *src) void init_cpu_possible(const struct cpumask *src) { cpumask_copy(&__cpu_possible_mask, src); + __num_possible_cpus = cpumask_weight(&__cpu_possible_mask); } void set_cpu_online(unsigned int cpu, bool online) @@ -3139,6 +3143,21 @@ void set_cpu_online(unsigned int cpu, bool online) } } +/* + * This should be marked __init, but there is a boatload of call sites + * which need to be fixed up to do so. Sigh... + */ +void set_cpu_possible(unsigned int cpu, bool possible) +{ + if (possible) { + if (!cpumask_test_and_set_cpu(cpu, &__cpu_possible_mask)) + __num_possible_cpus++; + } else { + if (cpumask_test_and_clear_cpu(cpu, &__cpu_possible_mask)) + __num_possible_cpus--; + } +} + /* * Activate the first processor. */ -- 2.47.3