Re: [PATCH 02/13] kernel/cpu: Add support for declaring CPU hotplug not supported

[Thomas Gleixner]

On Thu, Oct 05 2023 at 16:13, Kirill A. Shutemov wrote:
> The function cpu_hotplug_not_supported() can be called to indicate that
> CPU hotplug should be disabled. It does not prevent the initial bring up
> of the CPU, but it stops subsequent offlining.

This tells me what the patch is doing, but not the why.

> This function is intended to replace CC_ATTR_HOTPLUG_DISABLED.

> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -132,6 +132,7 @@ extern void cpus_read_lock(void);
>  extern void cpus_read_unlock(void);
>  extern int  cpus_read_trylock(void);
>  extern void lockdep_assert_cpus_held(void);
> +extern void cpu_hotplug_not_supported(void);

This function name sucks.

The point is as you explained to prevent offlining, but not onlining. So
can we please make this very clear? Something like:

    cpu_hotplug_disable_offlining()

> +/* Cleared if platform declares CPU hotplug not supported */
> +static bool cpu_hotplug_supported = true;

Again. This is not about disabling hotplug all together. Something like:

static bool cpu_hotplug_offline_disabled;

Which expresses clearly what this is about and does not require this
awkward negation.

Thanks,

        tglx