energy_model: use a fixed reference frequencysched/cpu_capacity

The last item of a performance domain is not always the performance point
that has been used to compute CPU's capacity. This can lead to different
target frequency compared with other part of the system like schedutil and
a a result wrong energy estimation.

a new arch_scale_freq_ref() is available to return a fixed and coherent
frequency reference that can be used when computing the CPU's frequency
for an level of utilization. Use this function when available or fallback
to the last performance domain item otherwise.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>

1 files changed, 17 insertions, 3 deletions

diff --git a/include/linux/energy_model.h b/include/linux/energy_model.h
index b9caa01dfac4..7ee07be6928e 100644
--- a/include/linux/energy_model.h
+++ b/include/linux/energy_model.h
@@ -204,6 +204,20 @@ struct em_perf_state *em_pd_get_efficient_state(struct em_perf_domain *pd,
 	return ps;
 }
 
+#ifdef arch_scale_freq_ref
+static __always_inline
+unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)
+{
+	return arch_scale_freq_ref(cpu);
+}
+#else
+static __always_inline
+unsigned long  arch_scale_freq_ref_em(int cpu, struct em_perf_domain *pd)
+{
+	return pd->table[pd->nr_perf_states - 1].frequency;
+}
+#endif
+
 /**
  * em_cpu_energy() - Estimates the energy consumed by the CPUs of a
  *		performance domain
@@ -224,7 +238,7 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
 				unsigned long max_util, unsigned long sum_util,
 				unsigned long allowed_cpu_cap)
 {
-	unsigned long freq, scale_cpu;
+	unsigned long freq, ref_freq, scale_cpu;
 	struct em_perf_state *ps;
 	int cpu;
 
@@ -241,11 +255,11 @@ static inline unsigned long em_cpu_energy(struct em_perf_domain *pd,
 	 */
 	cpu = cpumask_first(to_cpumask(pd->cpus));
 	scale_cpu = arch_scale_cpu_capacity(cpu);
-	ps = &pd->table[pd->nr_perf_states - 1];
+	ref_freq = arch_scale_freq_ref_em(cpu, pd);
 
 	max_util = map_util_perf(max_util);
 	max_util = min(max_util, allowed_cpu_cap);
-	freq = map_util_freq(max_util, ps->frequency, scale_cpu);
+	freq = map_util_freq(max_util, ref_freq, scale_cpu);
 
 	/*
 	 * Find the lowest performance state of the Energy Model above the