[PATCH v7 1/5] cpufreq/amd-pstate: Add dynamic energy performance preference

Mario Limonciello (AMD)
2026-03-31T19:59:17Z

Dynamic energy performance preference changes 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.

When enabled, the driver exposes a sysfs toggle for dynamic EPP, blocks
manual writes to energy_performance_preference, and keeps the policy in
performance mode while it "owns" the EPP updates.

For non-server systems:
* the default EPP for AC mode is `performance`.
* the default EPP for DC mode is `balance_performance`.

For server systems dynamic EPP is mostly a no-op.

Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
---
v6->v7:
* Fix accidental casualty of floor perf from rebase (Gautham)
* Adjust documentation (Gautham)
---
Documentation/admin-guide/pm/amd-pstate.rst | 18 ++-
drivers/cpufreq/Kconfig.x86 | 12 ++
drivers/cpufreq/amd-pstate.c | 131 +++++++++++++++++++-
drivers/cpufreq/amd-pstate.h | 10 +-
4 files changed, 163 insertions(+), 8 deletions(-)

diff --git a/Documentation/admin-guide/pm/amd-pstate.rst b/Documentation/admin-guide/pm/amd-pstate.rst
index b43675b7f739b..bb1341763882b 100644
--- a/Documentation/admin-guide/pm/amd-pstate.rst
+++ b/Documentation/admin-guide/pm/amd-pstate.rst
@@ -325,7 +325,7 @@ 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``
@@ -347,6 +347,22 @@ 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 depends on 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``.
+
+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``
======================================
diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
index 2c5c228408bf2..cdaa8d858045a 100644
--- a/drivers/cpufreq/Kconfig.x86
+++ b/drivers/cpufreq/Kconfig.x86
@@ -68,6 +68,18 @@ config X86_AMD_PSTATE_DEFAULT_MODE
For details, take a look at:
<file:Documentation/admin-guide/pm/amd-pstate.rst>.

+config X86_AMD_PSTATE_DYNAMIC_EPP
+ bool "AMD Processor P-State dynamic EPP support"
+ depends on X86_AMD_PSTATE
+ default n
+ help
+ Allow the kernel to dynamically change the energy performance
+ value from events like ACPI platform profile and AC adapter plug
+ events.
+
+ This feature can also be changed at runtime, this configuration
+ option only sets the kernel default value behavior.
+
config X86_AMD_PSTATE_UT
tristate "selftest for AMD Processor P-State driver"
depends on X86 && ACPI_PROCESSOR
diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
index f207252eb5f5f..d3c8eaab88286 100644
--- a/drivers/cpufreq/amd-pstate.c
+++ b/drivers/cpufreq/amd-pstate.c
@@ -36,6 +36,7 @@
#include <linux/io.h>
#include <linux/delay.h>
#include <linux/uaccess.h>
+#include <linux/power_supply.h>
#include <linux/static_call.h>
#include <linux/topology.h>

@@ -86,6 +87,11 @@ static struct cpufreq_driver amd_pstate_driver;
static struct cpufreq_driver amd_pstate_epp_driver;
static int cppc_state = AMD_PSTATE_UNDEFINED;
static bool amd_pstate_prefcore = true;
+#ifdef CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP
+static bool dynamic_epp = CONFIG_X86_AMD_PSTATE_DYNAMIC_EPP;
+#else
+static bool dynamic_epp;
+#endif
static struct quirk_entry *quirks;

/*
@@ -1155,6 +1161,74 @@ static void amd_pstate_cpu_exit(struct cpufreq_policy *policy)
kfree(cpudata);
}

+static int amd_pstate_get_balanced_epp(struct cpufreq_policy *policy)
+{
+ struct amd_cpudata *cpudata = policy->driver_data;
+
+ if (power_supply_is_system_supplied())
+ return cpudata->epp_default_ac;
+ else
+ return cpudata->epp_default_dc;
+}
+
+static int amd_pstate_power_supply_notifier(struct notifier_block *nb,
+ unsigned long event, void *data)
+{
+ struct amd_cpudata *cpudata = container_of(nb, struct amd_cpudata, power_nb);
+ struct cpufreq_policy *policy __free(put_cpufreq_policy) = cpufreq_cpu_get(cpudata->cpu);
+ u8 epp;
+ int ret;
+
+ if (event != PSY_EVENT_PROP_CHANGED)
+ return NOTIFY_OK;
+
+ epp = amd_pstate_get_balanced_epp(policy);
+
+ ret = amd_pstate_set_epp(policy, epp);
+ if (ret)
+ pr_warn("Failed to set CPU %d EPP %u: %d\n", cpudata->cpu, epp, ret);
+
+ return NOTIFY_OK;
+}
+static void amd_pstate_clear_dynamic_epp(struct cpufreq_policy *policy)
+{
+ struct amd_cpudata *cpudata = policy->driver_data;
+
+ if (cpudata->power_nb.notifier_call)
+ power_supply_unreg_notifier(&cpudata->power_nb);
+ cpudata->dynamic_epp = false;
+}
+
+static int amd_pstate_set_dynamic_epp(struct cpufreq_policy *policy)
+{
+ struct amd_cpudata *cpudata = policy->driver_data;
+ int ret;
+ u8 epp;
+
+ policy->policy = CPUFREQ_POLICY_PERFORMANCE;
+ epp = amd_pstate_get_balanced_epp(policy);
+ ret = amd_pstate_set_epp(policy, epp);
+ if (ret)
+ return ret;
+
+ /* only enable notifier if things will actually change */
+ if (cpudata->epp_default_ac != cpudata->epp_default_dc) {
+ cpudata->power_nb.notifier_call = amd_pstate_power_supply_notifier;
+ ret = power_supply_reg_notifier(&cpudata->power_nb);
+ if (ret)
+ goto cleanup;
+ }
+
+ cpudata->dynamic_epp = true;
+
+ return 0;
+
+cleanup:
+ amd_pstate_clear_dynamic_epp(policy);
+
+ return ret;
+}
+
/* Sysfs attributes */

/*
@@ -1244,14 +1318,19 @@ static ssize_t store_energy_performance_preference(
ssize_t ret;
u8 epp;

+ if (cpudata->dynamic_epp) {
+ pr_debug("EPP cannot be set when dynamic EPP is enabled\n");
+ return -EBUSY;
+ }
+
ret = sysfs_match_string(energy_perf_strings, buf);
if (ret < 0)
return -EINVAL;

- if (!ret)
- epp = cpudata->epp_default;
- else
+ if (ret)
epp = epp_values[ret];
+ else
+ epp = amd_pstate_get_balanced_epp(policy);

if (epp > 0 && policy->policy == CPUFREQ_POLICY_PERFORMANCE) {
pr_debug("EPP cannot be set under performance policy\n");
@@ -1259,6 +1338,8 @@ static ssize_t store_energy_performance_preference(
}

ret = amd_pstate_set_epp(policy, epp);
+ if (ret)
+ return ret;

return ret ? ret : count;
}
@@ -1620,12 +1701,40 @@ static ssize_t prefcore_show(struct device *dev,
return sysfs_emit(buf, "%s\n", str_enabled_disabled(amd_pstate_prefcore));
}

+static ssize_t dynamic_epp_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ return sysfs_emit(buf, "%s\n", str_enabled_disabled(dynamic_epp));
+}
+
+static ssize_t dynamic_epp_store(struct device *a, struct device_attribute *b,
+ const char *buf, size_t count)
+{
+ bool enabled;
+ int ret;
+
+ ret = kstrtobool(buf, &enabled);
+ if (ret)
+ return ret;
+
+ if (dynamic_epp == enabled)
+ return -EINVAL;
+
+ /* reinitialize with desired dynamic EPP value */
+ dynamic_epp = enabled;
+ ret = amd_pstate_change_driver_mode(cppc_state);
+
+ return ret ? ret : count;
+}
+
static DEVICE_ATTR_RW(status);
static DEVICE_ATTR_RO(prefcore);
+static DEVICE_ATTR_RW(dynamic_epp);

static struct attribute *pstate_global_attributes[] = {
&dev_attr_status.attr,
&dev_attr_prefcore.attr,
+ &dev_attr_dynamic_epp.attr,
NULL
};

@@ -1715,13 +1824,17 @@ static int amd_pstate_epp_cpu_init(struct cpufreq_policy *policy)
if (amd_pstate_acpi_pm_profile_server() ||
amd_pstate_acpi_pm_profile_undefined()) {
policy->policy = CPUFREQ_POLICY_PERFORMANCE;
- cpudata->epp_default = amd_pstate_get_epp(cpudata);
+ cpudata->epp_default_ac = cpudata->epp_default_dc = amd_pstate_get_epp(cpudata);
} else {
policy->policy = CPUFREQ_POLICY_POWERSAVE;
- cpudata->epp_default = AMD_CPPC_EPP_BALANCE_PERFORMANCE;
+ cpudata->epp_default_ac = AMD_CPPC_EPP_PERFORMANCE;
+ cpudata->epp_default_dc = AMD_CPPC_EPP_BALANCE_PERFORMANCE;
}

- ret = amd_pstate_set_epp(policy, cpudata->epp_default);
+ if (dynamic_epp)
+ ret = amd_pstate_set_dynamic_epp(policy);
+ else
+ ret = amd_pstate_set_epp(policy, amd_pstate_get_balanced_epp(policy));
if (ret)
goto free_cpudata1;

@@ -1753,6 +1866,8 @@ static void amd_pstate_epp_cpu_exit(struct cpufreq_policy *policy)
amd_pstate_update_perf(policy, perf.bios_min_perf, 0U, 0U, 0U, false);
amd_pstate_set_floor_perf(policy, cpudata->bios_floor_perf);

+ if (cpudata->dynamic_epp)
+ amd_pstate_clear_dynamic_epp(policy);
kfree(cpudata);
policy->driver_data = NULL;
}
@@ -1790,6 +1905,10 @@ 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, true);
diff --git a/drivers/cpufreq/amd-pstate.h b/drivers/cpufreq/amd-pstate.h
index 32b8b26ce388f..d929ae3163b3d 100644
--- a/drivers/cpufreq/amd-pstate.h
+++ b/drivers/cpufreq/amd-pstate.h
@@ -85,6 +85,11 @@ struct amd_aperf_mperf {
* AMD P-State driver supports preferred core featue.
* @epp_cached: Cached CPPC energy-performance preference value
* @policy: Cpufreq policy value
+ * @suspended: If CPU core if offlined
+ * @epp_default_ac: Default EPP value for AC power source
+ * @epp_default_dc: Default EPP value for DC power source
+ * @dynamic_epp: Whether dynamic EPP is enabled
+ * @power_nb: Notifier block for power events
*
* The amd_cpudata is key private data for each CPU thread in AMD P-State, and
* represents all the attributes and goals that AMD P-State requests at runtime.
@@ -118,7 +123,10 @@ 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;
};

/*
--
2.43.0