[PATCH v4 1/5] arch_topology: Introduce thermal pressure update function

[Lukasz Luba]

The thermal pressure is a mechanism which is used for providing
information about reduced CPU performance to the scheduler. Usually code
has to convert the value from frequency units into capacity units,
which are understandable by the scheduler. Create a common conversion code
which can be just used via a handy API.

Internally, the topology_update_thermal_pressure() operates on frequency
in MHz and max CPU frequency is taken from 'freq_factor' (per-cpu).

Signed-off-by: Lukasz Luba <lukasz.luba at arm.com>
---
 arch/arm/include/asm/topology.h   |  1 +
 arch/arm64/include/asm/topology.h |  1 +
 drivers/base/arch_topology.c      | 43 ++++++++++++++++++++++++++++++-
 include/linux/arch_topology.h     |  3 +++
 include/linux/sched/topology.h    |  7 +++++
 5 files changed, 54 insertions(+), 1 deletion(-)

diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
index 470299ee2fba..f1eafacc9a30 100644
--- a/arch/arm/include/asm/topology.h
+++ b/arch/arm/include/asm/topology.h
@@ -24,6 +24,7 @@
 /* Replace task scheduler's default thermal pressure API */
 #define arch_scale_thermal_pressure topology_get_thermal_pressure
 #define arch_set_thermal_pressure   topology_set_thermal_pressure
+#define arch_update_thermal_pressure	topology_update_thermal_pressure
 
 #else
 
diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
index ec2db3419c41..7a421cbc99ed 100644
--- a/arch/arm64/include/asm/topology.h
+++ b/arch/arm64/include/asm/topology.h
@@ -33,6 +33,7 @@ void update_freq_counters_refs(void);
 /* Replace task scheduler's default thermal pressure API */
 #define arch_scale_thermal_pressure topology_get_thermal_pressure
 #define arch_set_thermal_pressure   topology_set_thermal_pressure
+#define arch_update_thermal_pressure	topology_update_thermal_pressure
 
 #include <asm-generic/topology.h>
 
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index fc0836f460fb..bed7d502c9a1 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -25,6 +25,7 @@
 static DEFINE_PER_CPU(struct scale_freq_data __rcu *, sft_data);
 static struct cpumask scale_freq_counters_mask;
 static bool scale_freq_invariant;
+static DEFINE_PER_CPU(u32, freq_factor) = 1;
 
 static bool supports_scale_freq_counters(const struct cpumask *cpus)
 {
@@ -168,6 +169,47 @@ void topology_set_thermal_pressure(const struct cpumask *cpus,
 }
 EXPORT_SYMBOL_GPL(topology_set_thermal_pressure);
 
+/**
+ * topology_update_thermal_pressure() - Update thermal pressure for CPUs
+ * @cpus        : The related CPUs for which capacity has been reduced
+ * @capped_freq : The maximum allowed frequency that CPUs can run at
+ *
+ * Update the value of thermal pressure for all @cpus in the mask. The
+ * cpumask should include all (online+offline) affected CPUs, to avoid
+ * operating on stale data when hot-plug is used for some CPUs. The
+ * @capped_freq reflects the currently allowed max CPUs frequency due to
+ * thermal capping. It might be also a boost frequency value, which is bigger
+ * than the internal 'freq_factor' max frequency. In such case the pressure
+ * value should simply be removed, since this is an indication that there is
+ * no thermal throttling. The @capped_freq must be provided in kHz.
+ */
+void topology_update_thermal_pressure(const struct cpumask *cpus,
+				      unsigned long capped_freq)
+{
+	unsigned long max_capacity, capacity;
+	u32 max_freq;
+	int cpu;
+
+	cpu = cpumask_first(cpus);
+	max_capacity = arch_scale_cpu_capacity(cpu);
+	max_freq = per_cpu(freq_factor, cpu);
+
+	/* Convert to MHz scale which is used in 'freq_factor' */
+	capped_freq /= 1000;
+
+	/*
+	 * Handle properly the boost frequencies, which should simply clean
+	 * the thermal pressure value.
+	 */
+	if (max_freq <= capped_freq)
+		capacity = max_capacity;
+	else
+		capacity = mult_frac(max_capacity, capped_freq, max_freq);
+
+	arch_set_thermal_pressure(cpus, max_capacity - capacity);
+}
+EXPORT_SYMBOL_GPL(topology_update_thermal_pressure);
+
 static ssize_t cpu_capacity_show(struct device *dev,
 				 struct device_attribute *attr,
 				 char *buf)
@@ -220,7 +262,6 @@ static void update_topology_flags_workfn(struct work_struct *work)
 	update_topology = 0;
 }
 
-static DEFINE_PER_CPU(u32, freq_factor) = 1;
 static u32 *raw_capacity;
 
 static int free_raw_capacity(void)
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index b97cea83b25e..ace1e5dcf773 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -59,6 +59,9 @@ static inline unsigned long topology_get_thermal_pressure(int cpu)
 void topology_set_thermal_pressure(const struct cpumask *cpus,
 				   unsigned long th_pressure);
 
+void topology_update_thermal_pressure(const struct cpumask *cpus,
+				      unsigned long capped_freq);
+
 struct cpu_topology {
 	int thread_id;
 	int core_id;
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h
index c07bfa2d80f2..6e89a8e43aa7 100644
--- a/include/linux/sched/topology.h
+++ b/include/linux/sched/topology.h
@@ -273,6 +273,13 @@ void arch_set_thermal_pressure(const struct cpumask *cpus,
 { }
 #endif
 
+#ifndef arch_update_thermal_pressure
+static __always_inline
+void arch_update_thermal_pressure(const struct cpumask *cpus,
+				  unsigned long capped_frequency)
+{ }
+#endif
+
 static inline int task_node(const struct task_struct *p)
 {
 	return cpu_to_node(task_cpu(p));
-- 
2.17.1