drivers/base/arch_topology: Add infrastructure to store and update instantaneous thermal pressure
Add architecture specific APIs to update and track thermal pressure on a
per CPU basis. A per CPU variable thermal_pressure is introduced to keep
track of instantaneous per CPU thermal pressure. Thermal pressure is the
delta between maximum capacity and capped capacity due to a thermal event.
topology_get_thermal_pressure can be hooked into the scheduler specified
arch_scale_thermal_pressure to retrieve instantaneous thermal pressure of
a CPU.
arch_set_thermal_pressure can be used to update the thermal pressure.
Considering topology_get_thermal_pressure reads thermal_pressure and
arch_set_thermal_pressure writes into thermal_pressure, one can argue for
some sort of locking mechanism to avoid a stale value. But considering
topology_get_thermal_pressure can be called from a system critical path
like scheduler tick function, a locking mechanism is not ideal. This means
that it is possible the thermal_pressure value used to calculate average
thermal pressure for a CPU can be stale for up to 1 tick period.
Signed-off-by: Thara Gopinath <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index 3015ecbb..88a115e 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -33,6 +33,16 @@ unsigned long topology_get_freq_scale(int cpu)
return per_cpu(freq_scale, cpu);
}
+DECLARE_PER_CPU(unsigned long, thermal_pressure);
+
+static inline unsigned long topology_get_thermal_pressure(int cpu)
+{
+ return per_cpu(thermal_pressure, cpu);
+}
+
+void arch_set_thermal_pressure(struct cpumask *cpus,
+ unsigned long th_pressure);
+
struct cpu_topology {
int thread_id;
int core_id;
