linux-kernel - Re: [PATCH v7 06/16] ACPI: processor: Register deferred CPUs from acpi_processor_get

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Date: Fri, 26 Apr 2024 19:18:30 +1000
From: Gavin Shan <gshan@...hat.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra <peterz@...radead.org>,
 linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 kvmarm@...ts.linux.dev, x86@...nel.org, Russell King
 <linux@...linux.org.uk>, "Rafael J . Wysocki" <rafael@...nel.org>,
 Miguel Luis <miguel.luis@...cle.com>, James Morse <james.morse@....com>,
 Salil Mehta <salil.mehta@...wei.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>, linuxarm@...wei.com,
 justin.he@....com, jianyong.wu@....com
Subject: Re: [PATCH v7 06/16] ACPI: processor: Register deferred CPUs from
 acpi_processor_get_info()

On 4/18/24 23:54, Jonathan Cameron wrote:
> From: James Morse <james.morse@....com>
> 
> The arm64 specific arch_register_cpu() call may defer CPU registration
> until the ACPI interpreter is available and the _STA method can
> be evaluated.
> 
> If this occurs, then a second attempt is made in
> acpi_processor_get_info(). Note that the arm64 specific call has
> not yet been added so for now this will be called for the original
> hotplug case.
> 
> For architectures that do not defer until the ACPI Processor
> driver loads (e.g. x86), for initially present CPUs there will
> already be a CPU device. If present do not try to register again.
> 
> Systems can still be booted with 'acpi=off', or not include an
> ACPI description at all as in these cases arch_register_cpu()
> will not have deferred registration when first called.
> 
> This moves the CPU register logic back to a subsys_initcall(),
> while the memory nodes will have been registered earlier.
> Note this is where the call was prior to the cleanup series so
> there should be no side effects of moving it back again for this
> specific case.
> 
> [PATCH 00/21] Initial cleanups for vCPU HP.
> https://lore.kernel.org/all/ZVyz%2FVe5pPu8AWoA@shell.armlinux.org.uk/
> commit 5b95f94c3b9f ("x86/topology: Switch over to GENERIC_CPU_DEVICES")
> 
> Signed-off-by: James Morse <james.morse@....com>
> Reviewed-by: Gavin Shan <gshan@...hat.com>
> Tested-by: Miguel Luis <miguel.luis@...cle.com>
> Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@....com>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Co-developed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Signed-off-by: Joanthan Cameron <Jonathan.Cameron@...wei.com>
> ---

s/Joanthan/Jonathan ?

> v7: Simplify the logic on whether to hotadd the CPU.
>      This path can only be reached either for coldplug in which
>      case all we care about is has register_cpu() already been
>      called (identifying deferred), or hotplug in which case
>      whether register_cpu() has been called is also sufficient.
>      Checks on _STA related elements or the validity of the ID
>      are no longer necessary here due to similar checks having
>      moved elsewhere in the path.
> v6: Squash the two paths for conventional CPU Hotplug and arm64
>      vCPU HP.
> ---
>   drivers/acpi/acpi_processor.c | 14 +++++++-------
>   1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
> index 127ae8dcb787..4e65011e706c 100644
> --- a/drivers/acpi/acpi_processor.c
> +++ b/drivers/acpi/acpi_processor.c
> @@ -350,14 +350,14 @@ static int acpi_processor_get_info(struct acpi_device *device)
>   	}
>   
>   	/*
> -	 *  Extra Processor objects may be enumerated on MP systems with
> -	 *  less than the max # of CPUs. They should be ignored _iff
> -	 *  they are physically not present.
> -	 *
> -	 *  NOTE: Even if the processor has a cpuid, it may not be present
> -	 *  because cpuid <-> apicid mapping is persistent now.
> +	 *  This code is not called unless we know the CPU is present and
> +	 *  enabled. The two paths are:
> +	 *  a) Initially present CPUs on architectures that do not defer
> +	 *     their arch_register_cpu() calls until this point.
> +	 *  b) Hotplugged CPUs (enabled bit in _STA has transitioned from not
> +	 *     enabled to enabled)
>   	 */
> -	if (invalid_logical_cpuid(pr->id) || !cpu_present(pr->id)) {
> +	if (!get_cpu_device(pr->id)) {
>   		ret = acpi_processor_hotadd_init(pr, device);
>   
>   		if (ret)

Thanks,
Gavin