Re: [PATCH RFC v3 21/21] cpumask: Add enabled cpumask for present CPUs that can be brought online

Jonathan Cameron
2023-12-15T17:18:35Z

On Wed, 13 Dec 2023 12:50:59 +0000
Russell King (Oracle) <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
>
> 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.
>
> Signed-off-by: James Morse <james.morse@arm.com>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@arm.com>
> ---

Needs docs
Documentation/ABI/testing/sysfs-devices-system-cpu
seems to have the rest of the similar entries.

> Outstanding comment:
> https://lore.kernel.org/r/20230914175443.000038f6@Huawei.com
Very fussy reviewer. I'd ignore him on this :)

Code is fine.

Thanks for taking this forwards. Maybe the end of this saga is
close!

Jonathan

> ---
> 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 13d052bf13f4..a6e96a0a92b7 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 cfb545841a2c..cc72a0887f04 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)
> @@ -993,6 +996,7 @@ 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
>
> @@ -1015,6 +1019,15 @@ 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)
> {
> @@ -1096,6 +1109,7 @@ 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)
>
> @@ -1104,6 +1118,11 @@ 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);
> @@ -1128,6 +1147,7 @@ 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
>
> @@ -1141,6 +1161,11 @@ 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 a86972a91991..fe0a5189f8ae 100644
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -3122,6 +3122,9 @@ 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);
>