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

Russell King
2023-12-13T12:51:02Z

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>
---
Outstanding comment:
https://lore.kernel.org/r/20230914175443.000038f6@Huawei.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 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);

--
2.30.2