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

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index feba06eb0a42e77ae8cadac1b28356ddec77d392..66694ee8d86e924bde670a0bc9165c16810f417e 100644 (file)
--- 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 db9f6c539b28cef7cfae1d1fbb60b5f50ff7c10b..b674fdf96208be132a77d452d169f5353808dde4 100644 (file)
--- 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.
  */