linux-kernel - Re: [PATCH v9 19/19] cpumask: Add enabled cpumask for present CPUs that can be brought online

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Date: Wed, 1 May 2024 21:14:50 +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>,
 Marc Zyngier <maz@...nel.org>, Hanjun Guo <guohanjun@...wei.com>
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 v9 19/19] cpumask: Add enabled cpumask for present CPUs
 that can be brought online

On 5/1/24 00:24, Jonathan Cameron wrote:
> From: James Morse <james.morse@....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@....com>
> Tested-by: Miguel Luis <miguel.luis@...cle.com>
> Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
> Tested-by: Jianyong Wu <jianyong.wu@....com>
> Acked-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> 
> ---
> v9: 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(+)
> 

Reviewed-by: Gavin Shan <gshan@...hat.com>