Commit 35a5c37c authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

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: default avatarThomas Gleixner <tglx@linutronix.de>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarYury Norov <yury.norov@gmail.com>
Reviewed-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Reviewed-by: default avatarShrikanth Hegde <sshegde@linux.ibm.com>
Link: https://patch.msgid.link/20251119172549.578653738@linutronix.de
parent 79c11fb3

include/linux/cpumask.h

+8 −2
Original line number Diff line number Diff line
@@ -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)

kernel/cpu.c

+19 −0
Original line number Diff line number Diff line
@@ -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.

 */