RE: [PATCH v6 16/16] cpumask: Add enabled cpumask for present CPUs that can be brought online

Salil Mehta
2024-04-17T17:01:20Z

> From: Jonathan Cameron <jonathan.cameron@huawei.com>
> Sent: Wednesday, April 17, 2024 2:19 PM
>
> 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>
> Acked-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> ---
> v5: No change
> ---
> .../ABI/testing/sysfs-devices-system-cpu | 6 +++++
> drivers/base/cpu.c | 10 ++++++++
> include/linux/cpumask.h | 25 +++++++++++++++++++
> kernel/cpu.c | 3 +++
> 4 files changed, 44 insertions(+)
>

[...]

> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index
> b9d0d14e5960..4713b86d20f2 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);

sorry, It is being done here in context to (un)register)cpu().

> 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);

and here.

Thanks
Salil.