[RFC][PATCH v0.3 5/6] PM: EM: Introduce em_adjust_cpu_capacity()

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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

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_adjust_new_capacity()
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>
---

Note that this function is needed because the performance level values
in the EM "state" table need to be adjusted on CPU capacity changes.  In
the intel_pstate case the cost values associated with them don't change
because they are artificial anyway, so replacing the entire table just
in order to update the performance level values is a bit wasteful, but
it seems to be an exception (in the other cases when the CPU capacity
changes, the cost values change too AFAICS).

---
 include/linux/energy_model.h |    2 ++
 kernel/power/energy_model.c  |   28 ++++++++++++++++++++++++----
 2 files changed, 26 insertions(+), 4 deletions(-)

--- a/include/linux/energy_model.h
+++ b/include/linux/energy_model.h
@@ -179,6 +179,7 @@
 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 @@
 {
 	return -EINVAL;
 }
+void em_adjust_cpu_capacity(unsigned int cpu) {}
 static inline void em_rebuild_sched_domains(void) {}
 #endif
 
--- a/kernel/power/energy_model.c
+++ b/kernel/power/energy_model.c
@@ -698,10 +698,12 @@
 {
 	int ret;
 
-	ret = em_compute_costs(dev, em_table->state, NULL, pd->nr_perf_states,
-			       pd->flags);
-	if (ret)
-		goto free_em_table;
+	if (!(pd->flags & EM_PERF_DOMAIN_ARTIFICIAL)) {
+		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)
@@ -751,6 +753,24 @@
 	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;