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    SubjectRe: [RFC PATCH v2 35/35] cpumask: Add enabled cpumask for present CPUs that can be brought online
    On Wed, 13 Sep 2023 16:38:23 +0000
    James Morse <james.morse@arm.com> wrote:

    > The 'offline' file in sysfs shows all offline CPUs, including those
    > that aren't present. User-space is expected to remove not-present CPUs
    > from this list to learn which CPUs could be brought online.
    >
    > CPUs can be present but not-enabled. These CPUs can't be brought online
    > until the firmware policy changes, which comes with an ACPI notification
    > that will register the CPUs.
    >
    > With only the offline and present files, user-space is unable to
    > determine which CPUs it can try to bring online. Add a new CPU mask
    > that shows this based on all the registered CPUs.

    Bikeshed should be blue.

    Enabled is a really confusing name for this - to the extent that I'm not sure
    what it means. Assuming I have the sense right, how about the horrible
    onlineable or online_capable?


    >
    > Signed-off-by: James Morse <james.morse@arm.com>
    > ---
    > drivers/base/cpu.c | 10 ++++++++++
    > include/linux/cpumask.h | 25 +++++++++++++++++++++++++
    > kernel/cpu.c | 3 +++
    > 3 files changed, 38 insertions(+)
    >
    > diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
    > index c709747c4a18..a19a8be93102 100644
    > --- a/drivers/base/cpu.c
    > +++ b/drivers/base/cpu.c
    > @@ -95,6 +95,7 @@ void unregister_cpu(struct cpu *cpu)
    > {
    > int logical_cpu = cpu->dev.id;
    >
    > + set_cpu_enabled(logical_cpu, false);
    > unregister_cpu_under_node(logical_cpu, cpu_to_node(logical_cpu));
    >
    > device_unregister(&cpu->dev);
    > @@ -273,6 +274,13 @@ static ssize_t print_cpus_offline(struct device *dev,
    > }
    > static DEVICE_ATTR(offline, 0444, print_cpus_offline, NULL);
    >
    > +static ssize_t print_cpus_enabled(struct device *dev,
    > + struct device_attribute *attr, char *buf)
    > +{
    > + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_enabled_mask));
    > +}
    > +static DEVICE_ATTR(enabled, 0444, print_cpus_enabled, NULL);
    > +
    > static ssize_t print_cpus_isolated(struct device *dev,
    > struct device_attribute *attr, char *buf)
    > {
    > @@ -413,6 +421,7 @@ int register_cpu(struct cpu *cpu, int num)
    > register_cpu_under_node(num, cpu_to_node(num));
    > dev_pm_qos_expose_latency_limit(&cpu->dev,
    > PM_QOS_RESUME_LATENCY_NO_CONSTRAINT);
    > + set_cpu_enabled(num, true);
    >
    > return 0;
    > }
    > @@ -494,6 +503,7 @@ static struct attribute *cpu_root_attrs[] = {
    > &cpu_attrs[2].attr.attr,
    > &dev_attr_kernel_max.attr,
    > &dev_attr_offline.attr,
    > + &dev_attr_enabled.attr,
    > &dev_attr_isolated.attr,
    > #ifdef CONFIG_NO_HZ_FULL
    > &dev_attr_nohz_full.attr,
    > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
    > index f10fb87d49db..a29ee03f13ff 100644
    > --- a/include/linux/cpumask.h
    > +++ b/include/linux/cpumask.h
    > @@ -92,6 +92,7 @@ static inline void set_nr_cpu_ids(unsigned int nr)
    > *
    > * cpu_possible_mask- has bit 'cpu' set iff cpu is populatable
    > * cpu_present_mask - has bit 'cpu' set iff cpu is populated
    > + * cpu_enabled_mask - has bit 'cpu' set iff cpu can be brought online
    > * cpu_online_mask - has bit 'cpu' set iff cpu available to scheduler
    > * cpu_active_mask - has bit 'cpu' set iff cpu available to migration
    > *
    > @@ -124,11 +125,13 @@ static inline void set_nr_cpu_ids(unsigned int nr)
    >
    > extern struct cpumask __cpu_possible_mask;
    > extern struct cpumask __cpu_online_mask;
    > +extern struct cpumask __cpu_enabled_mask;
    > extern struct cpumask __cpu_present_mask;
    > extern struct cpumask __cpu_active_mask;
    > extern struct cpumask __cpu_dying_mask;
    > #define cpu_possible_mask ((const struct cpumask *)&__cpu_possible_mask)
    > #define cpu_online_mask ((const struct cpumask *)&__cpu_online_mask)
    > +#define cpu_enabled_mask ((const struct cpumask *)&__cpu_enabled_mask)
    > #define cpu_present_mask ((const struct cpumask *)&__cpu_present_mask)
    > #define cpu_active_mask ((const struct cpumask *)&__cpu_active_mask)
    > #define cpu_dying_mask ((const struct cpumask *)&__cpu_dying_mask)
    > @@ -973,6 +976,7 @@ extern const DECLARE_BITMAP(cpu_all_bits, NR_CPUS);
    > #else
    > #define for_each_possible_cpu(cpu) for_each_cpu((cpu), cpu_possible_mask)
    > #define for_each_online_cpu(cpu) for_each_cpu((cpu), cpu_online_mask)
    > +#define for_each_enabled_cpu(cpu) for_each_cpu((cpu), cpu_enabled_mask)
    > #define for_each_present_cpu(cpu) for_each_cpu((cpu), cpu_present_mask)
    > #endif
    >
    > @@ -995,6 +999,15 @@ set_cpu_possible(unsigned int cpu, bool possible)
    > cpumask_clear_cpu(cpu, &__cpu_possible_mask);
    > }
    >
    > +static inline void
    > +set_cpu_enabled(unsigned int cpu, bool can_be_onlined)
    > +{
    > + if (can_be_onlined)
    > + cpumask_set_cpu(cpu, &__cpu_enabled_mask);
    > + else
    > + cpumask_clear_cpu(cpu, &__cpu_enabled_mask);
    > +}
    > +
    > static inline void
    > set_cpu_present(unsigned int cpu, bool present)
    > {
    > @@ -1074,6 +1087,7 @@ 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)
    > +#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)
    >
    > @@ -1082,6 +1096,11 @@ static inline bool cpu_online(unsigned int cpu)
    > return cpumask_test_cpu(cpu, cpu_online_mask);
    > }
    >
    > +static inline bool cpu_enabled(unsigned int cpu)
    > +{
    > + return cpumask_test_cpu(cpu, cpu_enabled_mask);
    > +}
    > +
    > static inline bool cpu_possible(unsigned int cpu)
    > {
    > return cpumask_test_cpu(cpu, cpu_possible_mask);
    > @@ -1106,6 +1125,7 @@ static inline bool cpu_dying(unsigned int cpu)
    >
    > #define num_online_cpus() 1U
    > #define num_possible_cpus() 1U
    > +#define num_enabled_cpus() 1U
    > #define num_present_cpus() 1U
    > #define num_active_cpus() 1U
    >
    > @@ -1119,6 +1139,11 @@ static inline bool cpu_possible(unsigned int cpu)
    > return cpu == 0;
    > }
    >
    > +static inline bool cpu_enabled(unsigned int cpu)
    > +{
    > + return cpu == 0;
    > +}
    > +
    > static inline bool cpu_present(unsigned int cpu)
    > {
    > return cpu == 0;
    > diff --git a/kernel/cpu.c b/kernel/cpu.c
    > index 6de7c6bb74ee..2201a6a449b5 100644
    > --- a/kernel/cpu.c
    > +++ b/kernel/cpu.c
    > @@ -3101,6 +3101,9 @@ EXPORT_SYMBOL(__cpu_possible_mask);
    > struct cpumask __cpu_online_mask __read_mostly;
    > EXPORT_SYMBOL(__cpu_online_mask);
    >
    > +struct cpumask __cpu_enabled_mask __read_mostly;
    > +EXPORT_SYMBOL(__cpu_enabled_mask);
    > +
    > struct cpumask __cpu_present_mask __read_mostly;
    > EXPORT_SYMBOL(__cpu_present_mask);
    >

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