Re: [PATCH RFC 01/22] arch_topology: Make register_cpu_capacity_sysctl() tolerant to late CPUs

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 07 Nov 2023 10:29:23 +0000
Russell King <rmk+kernel@armlinux.org.uk> wrote:

> From: James Morse <james.morse@arm.com>
> 
> register_cpu_capacity_sysctl() adds a property to sysfs that describes
> the CPUs capacity. This is done from a subsys_initcall() that assumes
> all possible CPUs are registered.
> 
> With CPU hotplug, possible CPUs aren't registered until they become
> present, (or for arm64 enabled). This leads to messages during boot:
> | register_cpu_capacity_sysctl: too early to get CPU1 device!
> and once these CPUs are added to the system, the file is missing.
> 
> Move this to a cpuhp callback, so that the file is created once
> CPUs are brought online. This covers CPUs that are added late by
> mechanisms like hotplug.
> One observable difference is the file is now missing for offline CPUs.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
> If the offline CPUs thing is a problem for the tools that consume
> this value, we'd need to move cpu_capacity to be part of cpu.c's
> common_cpu_attr_groups.

I'm not keen on squirting sysfs files in from code so
might be nice to do that anyway and use is_visible() / sysfs_update_group()
but that would be a job for another day if at all.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>