linux-kernel - [PATCH v1] PM: EM: Add function for registering a PD without capacity update

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Message-ID: <5939134.DvuYhMxLoT@rafael.j.wysocki>
Date: Fri, 05 Sep 2025 15:44:45 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: Lukasz Luba <lukasz.luba@....com>, LKML <linux-kernel@...r.kernel.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Christian Loehle <christian.loehle@....com>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 "Kenneth R. Crudup" <kenny@...ix.com>
Subject:
 [PATCH v1] PM: EM: Add function for registering a PD without capacity update

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

The intel_pstate driver manages CPU capacity changes itself and it does
not need an update of the capacity of all CPUs in the system to be
carried out after registering a PD.

Moreover, in some configurations (for instance, an SMT-capable
hybrid x86 system booted with nosmt in the kernel command line) the
em_check_capacity_update() call at the end of em_dev_register_perf_domain()
always fails and reschedules itself to run once again in 1 s, so
effectively it runs in vain every 1 s forever.

To address this, introduce a new variant of em_dev_register_perf_domain(),
called em_dev_register_pd_no_update(), that does not invoke
em_check_capacity_update(), and make intel_pstate use it instead of the
original.

Fixes: 7b010f9b9061 ("cpufreq: intel_pstate: EAS support for hybrid platforms")
Link: https://lore.kernel.org/linux-pm/40212796-734c-4140-8a85-854f72b8144d@panix.com/
Reported-by: Kenneth R. Crudup <kenny@...ix.com>
Tested-by: Kenneth R. Crudup <kenny@...ix.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: 6.16+ <stable@...r.kernel.org> # 6.16+
---

Normally, I would place the definition of em_dev_register_pd_no_update()
before the definition of em_dev_register_perf_domain() which called it,
but in this particular case that would cause the real change to be much
harder to grasp.

---
 drivers/cpufreq/intel_pstate.c |    4 ++--
 include/linux/energy_model.h   |   10 ++++++++++
 kernel/power/energy_model.c    |   29 +++++++++++++++++++++++++----
 3 files changed, 37 insertions(+), 6 deletions(-)

--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1034,8 +1034,8 @@ static bool hybrid_register_perf_domain(
 	if (!cpu_dev)
 		return false;
 
-	if (em_dev_register_perf_domain(cpu_dev, HYBRID_EM_STATE_COUNT, &cb,
-					cpumask_of(cpu), false))
+	if (em_dev_register_pd_no_update(cpu_dev, HYBRID_EM_STATE_COUNT, &cb,
+					 cpumask_of(cpu), false))
 		return false;
 
 	cpudata->pd_registered = true;
--- a/include/linux/energy_model.h
+++ b/include/linux/energy_model.h
@@ -171,6 +171,9 @@ int em_dev_update_perf_domain(struct dev
 int em_dev_register_perf_domain(struct device *dev, unsigned int nr_states,
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts);
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts);
 void em_dev_unregister_perf_domain(struct device *dev);
 struct em_perf_table *em_table_alloc(struct em_perf_domain *pd);
 void em_table_free(struct em_perf_table *table);
@@ -350,6 +353,13 @@ int em_dev_register_perf_domain(struct d
 {
 	return -EINVAL;
 }
+static inline
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts)
+{
+	return -EINVAL;
+}
 static inline void em_dev_unregister_perf_domain(struct device *dev)
 {
 }
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -553,6 +553,30 @@ int em_dev_register_perf_domain(struct d
 				const struct em_data_callback *cb,
 				const cpumask_t *cpus, bool microwatts)
 {
+	int ret = em_dev_register_pd_no_update(dev, nr_states, cb, cpus, microwatts);
+
+	if (_is_cpu_device(dev))
+		em_check_capacity_update();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
+
+/**
+ * em_dev_register_pd_no_update() - Register a perf domain for a device
+ * @dev : Device to register the PD for
+ * @nr_states : Number of performance states in the new PD
+ * @cb : Callback functions for populating the energy model
+ * @cpus : CPUs to include in the new PD (mandatory if @dev is a CPU device)
+ * @microwatts : Whether or not the power values in the EM will be in uW
+ *
+ * Like em_dev_register_perf_domain(), but does not trigger a CPU capacity
+ * update after registering the PD, even if @dev is a CPU device.
+ */
+int em_dev_register_pd_no_update(struct device *dev, unsigned int nr_states,
+				 const struct em_data_callback *cb,
+				 const cpumask_t *cpus, bool microwatts)
+{
 	struct em_perf_table *em_table;
 	unsigned long cap, prev_cap = 0;
 	unsigned long flags = 0;
@@ -636,12 +660,9 @@ int em_dev_register_perf_domain(struct d
 unlock:
 	mutex_unlock(&em_pd_mutex);
 
-	if (_is_cpu_device(dev))
-		em_check_capacity_update();
-
 	return ret;
 }
-EXPORT_SYMBOL_GPL(em_dev_register_perf_domain);
+EXPORT_SYMBOL_GPL(em_dev_register_pd_no_update);
 
 /**
  * em_dev_unregister_perf_domain() - Unregister Energy Model (EM) for a device