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

[Mario Limonciello]

On 3/24/2025 03:19, Dhananjay Ugwekar wrote:
> On 3/21/2025 7:58 AM, Mario Limonciello wrote:
> > From: Mario Limonciello <mario.limonciello@xxxxxxx>
> >
> > 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@xxxxxxx>
> > ---
> > 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;
> >   };
> >   
> >   /*