Re: [Patch 0/5] Support Autonomous Selection mode in cppc_cpufreq

Sumit Gupta
2025-02-11T14:09:17Z

>
> On 2025/2/11 18:44, Viresh Kumar wrote:
>> On 11-02-25, 16:07, Sumit Gupta wrote:
>>> This patchset supports the Autonomous Performance Level Selection mode
>>> in the cppc_cpufreq driver. The feature is part of the existing CPPC
>>> specification and already present in Intel and AMD specific pstate
>>> cpufreq drivers. The patchset adds the support in generic acpi cppc
>>> cpufreq driver.
>>
>> Is there an overlap with:
>>
>> https://lore.kernel.org/all/20250206131428.3261578-1-zhenglifeng1@huawei.com/
>>
>> ?
>
> Ha, it looks like we're doing something very similar.
>

Hi Viresh,

Thank you for pointing to [1].

There seems to be some common points about updating the 'energy_perf'
and 'auto_sel' registers for autonomous mode but the current patchset
has more comprehensive changes to support Autonomous mode with the
cppc_cpufreq driver.

The patches in [1]:
1) Make the cpc register read/write API’s generic and improves error
handling for 'CPC_IN_PCC'.
2) Expose sysfs under 'cppc_cpufreq_attr' to update 'auto_select',
'auto_act_window' and 'epp' registers.

The current patch series:
1) Exposes sysfs under 'cppc_attrs' to keep CPC registers together.
2) Updates existing API’s to use new registers and creates new API
with similar semantics to get all perf_ctrls.
3) Renames some existing API’s for clarity.
4) Use these existing API’s from acpi_cppc sysfs to update the CPC
registers used in Autonomous mode:
'auto_select', 'epp', 'min_perf', 'max_perf' registers.
5) Add separate 'cppc_cpufreq_epp' instance of the 'cppc_cpufreq'
driver to apply different limit and policy for Autonomous mode.
Having it separate will avoid confusion between SW and HW mode.
Also, it will be easy to scale and add new features in future
without interference. Similar approach is used in Intel and AMD
pstate drivers.

Please share inputs about the preferred approach.

Best Regards,
Sumit Gupta

[1]
https://lore.kernel.org/all/20250206131428.3261578-1-zhenglifeng1@huawei.com/

>>
>>> It adds a new 'cppc_cpufreq_epp' instance of the 'cppc_cpufreq' driver
>>> for supporting the Autonomous Performance Level Selection and Energy
>>> Performance Preference (EPP).
>>> Autonomous selection will get enabled during boot if 'cppc_auto_sel'
>>> boot argument is passed or the 'Autonomous Selection Enable' register
>>> is already set before kernel boot. When enabled, the hardware is
>>> allowed to autonomously select the CPU frequency within the min and
>>> max perf boundaries using the Engergy Performance Preference hints.
>>> The EPP values range from '0x0'(performance preference) to '0xFF'
>>> (energy efficiency preference).
>>>
>>> It also exposes the acpi_cppc sysfs nodes to update the epp, auto_sel
>>> and {min|max_perf} registers for changing the hints to hardware for
>>> Autonomous selection.
>>>
>>> In a followup patch, plan to add support to dynamically switch the
>>> cpufreq driver instance from 'cppc_cpufreq_epp' to 'cppc_cpufreq' and
>>> vice-versa without reboot.
>>>
>>> The patches are divided into below groups:
>>> - Patch [1-2]: Improvements. Can be applied independently.
>>> - Patch [3-4]: sysfs store nodes for Auto mode. Depend on Patch [1-2].
>>> - Patch [5]: Support for 'cppc_cpufreq_epp'. Uses a macro from [3].
>>>
>>> Sumit Gupta (5):
>>> ACPI: CPPC: add read perf ctrls api and rename few existing
>>> ACPI: CPPC: expand macro to create store acpi_cppc sysfs node
>>> ACPI: CPPC: support updating epp, auto_sel and {min|max_perf} from
>>> sysfs
>>> Documentation: ACPI: add autonomous mode ctrls info in cppc_sysfs.txt
>>> cpufreq: CPPC: Add cppc_cpufreq_epp instance for Autonomous mode
>>>
>>> Documentation/admin-guide/acpi/cppc_sysfs.rst | 28 ++
>>> .../admin-guide/kernel-parameters.txt | 11 +
>>> drivers/acpi/cppc_acpi.c | 311 ++++++++++++++++--
>>> drivers/cpufreq/cppc_cpufreq.c | 260 ++++++++++++++-
>>> include/acpi/cppc_acpi.h | 19 +-
>>> 5 files changed, 572 insertions(+), 57 deletions(-)
>>
>