arch_topology: Introduce minimum frequency scale

The scheduler is unaware of the applied min_freq limit to a CPU, which is
useful information when predicting the frequency a CPU will run at for
energy efficiency purposes.

Export this information via arch_scale_min_freq_capacity() and wire it up
for arm64.

Change-Id: Icdff7628c095185280e95dd965d497e6f740c871
Signed-off-by: Sultan Alsawaf <sultan@kerneltoast.com>
Signed-off-by: Richard Raya <rdxzv.dev@gmail.com>

arch/arm64/include/asm/topology.h

@@ -47,6 +47,12 @@ int pcibus_to_node(struct pci_bus *bus);
 /* Enable topology flag updates */
 #define arch_update_cpu_topology topology_update_cpu_topology
 
+/* Define function to set the minimum frequency scaling factor */
+#define arch_set_min_freq_scale topology_set_min_freq_scale
+
+/* Define function to get the minimum frequency scaling factor */
+#define arch_scale_min_freq_capacity topology_get_min_freq_scale
+
 #include <asm-generic/topology.h>
 
 #endif /* _ASM_ARM_TOPOLOGY_H */

drivers/base/arch_topology.c

@@ -106,6 +106,24 @@ void arch_set_max_freq_scale(struct cpumask *cpus,
 		per_cpu(max_freq_scale, cpu) = scale;
 }
 
+DEFINE_PER_CPU(unsigned long, arch_min_freq_scale);
+EXPORT_PER_CPU_SYMBOL_GPL(arch_min_freq_scale);
+
+void topology_set_min_freq_scale(const struct cpumask *cpus,
+				 unsigned long min_freq, unsigned long max_freq)
+{
+	unsigned long scale;
+	int i;
+
+	if (WARN_ON_ONCE(!max_freq))
+		return;
+
+	scale = (min_freq * per_cpu(cpu_scale, cpumask_any(cpus))) / max_freq;
+
+	for_each_cpu(i, cpus)
+		per_cpu(arch_min_freq_scale, i) = scale;
+}
+
 static DEFINE_MUTEX(cpu_scale_mutex);
 DEFINE_PER_CPU(unsigned long, cpu_scale) = SCHED_CAPACITY_SCALE;
 

drivers/cpufreq/cpufreq.c

@@ -2282,6 +2282,9 @@ static int cpufreq_set_policy(struct cpufreq_policy *policy,
 
 	trace_cpu_frequency_limits(policy->max, policy->min, policy->cpu);
 
+	arch_set_min_freq_scale(policy->related_cpus, policy->min,
+				policy->cpuinfo.max_freq);
+
 	policy->cached_target_freq = UINT_MAX;
 
 	pr_debug("new min and max freqs are %u - %u kHz\n",

include/linux/arch_topology.h

@@ -44,6 +44,16 @@ unsigned long topology_get_freq_scale(struct sched_domain *sd, int cpu)
 	return per_cpu(freq_scale, cpu);
 }
 
+DECLARE_PER_CPU(unsigned long, arch_min_freq_scale);
+
+static inline unsigned long topology_get_min_freq_scale(int cpu)
+{
+	return per_cpu(arch_min_freq_scale, cpu);
+}
+
+void topology_set_min_freq_scale(const struct cpumask *cpus,
+				 unsigned long min_freq, unsigned long max_freq);
+
 DECLARE_PER_CPU(unsigned long, max_freq_scale);
 DECLARE_PER_CPU(unsigned long, max_thermal_scale);
 

include/linux/cpufreq.h

@@ -923,6 +923,14 @@ extern void arch_set_max_freq_scale(struct cpumask *cpus,
 				    unsigned long policy_max_freq);
 extern void arch_set_max_thermal_scale(struct cpumask *cpus,
 					unsigned long max_thermal_freq);
+#ifndef arch_set_min_freq_scale
+static __always_inline
+void arch_set_min_freq_scale(const struct cpumask *cpus,
+			     unsigned long min_freq,
+			     unsigned long max_freq)
+{
+}
+#endif
 /* the following are really really optional */
 extern struct freq_attr cpufreq_freq_attr_scaling_available_freqs;
 extern struct freq_attr cpufreq_freq_attr_scaling_boost_freqs;

kernel/sched/sched.h

@@ -2029,6 +2029,14 @@ unsigned long arch_scale_cpu_capacity(struct sched_domain *sd, int cpu)
 }
 #endif
 
+#ifndef arch_scale_min_freq_capacity
+static __always_inline
+unsigned long arch_scale_min_freq_capacity(int cpu)
+{
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_SMP
 static inline unsigned long capacity_of(int cpu)
 {