PM: EM: Introduce em_adjust_cpu_capacity()

JIRA: https://issues.redhat.com/browse/RHEL-110833

commit 4a6b1cf
Author: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Date:   Tue May 6 22:41:21 2025 +0200

    PM: EM: Introduce em_adjust_cpu_capacity()

    Add a function for updating the Energy Model for a CPU after its
    capacity has changed, which subsequently will be used by the
    intel_pstate driver.

    An EM_PERF_DOMAIN_ARTIFICIAL check is added to em_recalc_and_update()
    to prevent it from calling em_compute_costs() for an "artificial" perf
    domain with a NULL cb parameter which would cause it to crash.

    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
    Reviewed-by: Lukasz Luba <lukasz.luba@arm.com>
    Tested-by: Christian Loehle <christian.loehle@arm.com>
    Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
    Link: https://patch.msgid.link/3637203.iIbC2pHGDl@rjwysocki.net

Signed-off-by: Steve Best <sbest@redhat.com>

Author: sfbest

include/linux/energy_model.h

@@ -179,6 +179,7 @@ int em_dev_compute_costs(struct device *dev, struct em_perf_state *table,
 int em_dev_update_chip_binning(struct device *dev);
 int em_update_performance_limits(struct em_perf_domain *pd,
 		unsigned long freq_min_khz, unsigned long freq_max_khz);
+void em_adjust_cpu_capacity(unsigned int cpu);
 void em_rebuild_sched_domains(void);
 
 /**
@@ -405,6 +406,7 @@ int em_update_performance_limits(struct em_perf_domain *pd,
 {
 	return -EINVAL;
 }
+static inline void em_adjust_cpu_capacity(unsigned int cpu) {}
 static inline void em_rebuild_sched_domains(void) {}
 #endif
 

kernel/power/energy_model.c

@@ -702,10 +702,12 @@ static int em_recalc_and_update(struct device *dev, struct em_perf_domain *pd,
 {
 	int ret;
 
-	ret = em_compute_costs(dev, em_table->state, NULL, pd->nr_perf_states,
-			       pd->flags);
-	if (ret)
-		goto free_em_table;
+	if (!em_is_artificial(pd)) {
+		ret = em_compute_costs(dev, em_table->state, NULL,
+				       pd->nr_perf_states, pd->flags);
+		if (ret)
+			goto free_em_table;
+	}
 
 	ret = em_dev_update_perf_domain(dev, em_table);
 	if (ret)
@@ -755,6 +757,24 @@ static void em_adjust_new_capacity(unsigned int cpu, struct device *dev,
 	em_recalc_and_update(dev, pd, em_table);
 }
 
+/**
+ * em_adjust_cpu_capacity() - Adjust the EM for a CPU after a capacity update.
+ * @cpu: Target CPU.
+ *
+ * Adjust the existing EM for @cpu after a capacity update under the assumption
+ * that the capacity has been updated in the same way for all of the CPUs in
+ * the same perf domain.
+ */
+void em_adjust_cpu_capacity(unsigned int cpu)
+{
+	struct device *dev = get_cpu_device(cpu);
+	struct em_perf_domain *pd;
+
+	pd = em_pd_get(dev);
+	if (pd)
+		em_adjust_new_capacity(cpu, dev, pd);
+}
+
 static void em_check_capacity_update(void)
 {
 	cpumask_var_t cpu_done_mask;