Re: [PATCH v4 1/5] cpufreq/amd-pstate: Add dynamic energy performance preference

[Mario Limonciello <superm1@kernel.org>]

On 3/24/2025 03:19, Dhananjay Ugwekar wrote:
> On 3/21/2025 7:58 AM, Mario Limonciello wrote:
>> From: Mario Limonciello <mario.limonciello@amd.com>
>>
>> Dynamic energy performance preference will change the EPP profile
>> based on whether the machine is running on AC or DC power.
>>
>> A notification chain from the power supply core is used to adjust
>> EPP values on plug in or plug out events.
>>
>> For non-server systems:
>>      * the default EPP for AC mode is `performance`.
>>      * the default EPP for DC mode is `balance_performance`.
>>
>> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
>> ---
>> v3->v4:
>>   * Handle Kconfig not being set
>>   * Fix dynamic epp default on server
>> v2-v3:
>>   * Fix typo in Kconfig
>> v1->v2:
>>   * Change defaults to performance (AC) and balance_performance (DC)
>>   * Default Kconfig to disabled for now
>>   * Rebase on latest branch
>> ---
>>   Documentation/admin-guide/pm/amd-pstate.rst |  18 ++-
>>   drivers/cpufreq/Kconfig.x86                 |  12 ++
>>   drivers/cpufreq/amd-pstate.c                | 135 +++++++++++++++++++-
>>   drivers/cpufreq/amd-pstate.h                |   5 +-
>>   4 files changed, 161 insertions(+), 9 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
>> index 412423c54f258..2e076650dc77c 100644
>> --- a/Documentation/admin-guide/pm/amd-pstate.rst
>> +++ b/Documentation/admin-guide/pm/amd-pstate.rst
>> @@ -289,7 +289,7 @@ and user can change current preference according to energy or performance needs
>>   Please get all support profiles list from
>>   ``energy_performance_available_preferences`` attribute, all the profiles are
>>   integer values defined between 0 to 255 when EPP feature is enabled by platform
>> -firmware, if EPP feature is disabled, driver will ignore the written value
>> +firmware, but if the dynamic EPP feature is enabled, driver will block writes.
>>   This attribute is read-write.
>>   
>>   ``boost``
>> @@ -311,6 +311,22 @@ boost or `1` to enable it, for the respective CPU using the sysfs path
>>   Other performance and frequency values can be read back from
>>   ``/sys/devices/system/cpu/cpuX/acpi_cppc/``, see :ref:`cppc_sysfs`.
>>   
>> +Dynamic energy performance profile
>> +==================================
>> +The amd-pstate driver supports dynamically selecting the energy performance
>> +profile based on whether the machine is running on AC or DC power.
>> +
>> +Whether this behavior is enabled by default with the kernel config option
>> +`CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP`. This behavior can also be overridden
>> +at runtime by the sysfs file ``/sys/devices/system/cpu/cpufreq/policyX/dynamic_epp``.
> 
> The file is actually located at "/sys/devices/system/cpu/amd_pstate/dynamic_epp"
> 
>> +
>> +When set to enabled, the driver will select a different energy performance
>> +profile when the machine is running on battery or AC power.
>> +When set to disabled, the driver will not change the energy performance profile
>> +based on the power source and will not react to user desired power state.
>> +
>> +Attempting to manually write to the ``energy_performance_preference`` sysfs
>> +file will fail when ``dynamic_epp`` is enabled.
>>   
>>   ``amd-pstate`` vs ``acpi-cpufreq``
>>   ======================================
> [snip]
>> @@ -1502,9 +1611,15 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
>>   			return ret;
>>   		WRITE_ONCE(cpudata->cppc_req_cached, value);
>>   	}
>> -	ret = amd_pstate_set_epp(policy, cpudata->epp_default);
>> +
>> +	if (dynamic_epp) {
>> +		policy->policy = CPUFREQ_POLICY_PERFORMANCE;
> 
> So, we are allowing the dynamic EPP framework to modify the EPP value in performance
> governor as well? Shouldn't we allow dynamic_epp only with powersave governor.

You're right; I was trying to avoid issues in 
amd_pstate_epp_set_policy() but I'll come up with a way to correct this.

> 
>> +		ret = amd_pstate_set_dynamic_epp(policy);
>> +	}
>> +	else
>> +		ret = amd_pstate_set_epp(policy, amd_pstate_get_balanced_epp(policy));
>>   	if (ret)
>> -		return ret;
>> +		goto free_cpudata1;
>>   
>>   	current_pstate_driver->adjust_perf = NULL;
>>   
>> @@ -1521,6 +1636,8 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
>>   	struct amd_cpudata *cpudata = policy->driver_data;
>>   
>>   	if (cpudata) {
>> +		if (cpudata->dynamic_epp)
>> +			amd_pstate_clear_dynamic_epp(policy);
>>   		kfree(cpudata);
>>   		policy->driver_data = NULL;
>>   	}
>> @@ -1556,6 +1673,10 @@ static int amd_pstate_epp_set_policy(struct cpufreq_policy *policy)
>>   	if (!policy->cpuinfo.max_freq)
>>   		return -ENODEV;
>>   
>> +	/* policy can't be changed to powersave policy while dynamic epp is enabled */
>> +	if (policy->policy == CPUFREQ_POLICY_POWERSAVE && cpudata->dynamic_epp)
>> +		return -EBUSY;
>> +
>>   	cpudata->policy = policy->policy;
>>   
>>   	ret = amd_pstate_epp_update_limit(policy);
>> diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
>> index fbe1c08d3f061..6882876f895de 100644
>> --- a/drivers/cpufreq/amd-pstate.h
>> +++ b/drivers/cpufreq/amd-pstate.h
>> @@ -104,7 +104,10 @@ struct amd_cpudata {
>>   	/* EPP feature related attributes*/
>>   	u32	policy;
>>   	bool	suspended;
>> -	u8	epp_default;
>> +	u8	epp_default_ac;
>> +	u8	epp_default_dc;
>> +	bool	dynamic_epp;
>> +	struct notifier_block power_nb;
>>   };
>>   
>>   /*
>