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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 <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: Shrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20251119172549.578653738@linutronix.de
This commit is contained in:
Thomas Gleixner 2025-11-19 18:27:01 +01:00
parent 79c11fb3da
commit 35a5c37cb9
2 changed files with 27 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
include/linux/cpumask.h
View File

@ -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)

19
kernel/cpu.c
View File

@ -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.
*/