From ad58cc5cc50ca8423cf630778594bd38252a0a58 Mon Sep 17 00:00:00 2001 From: Thara Gopinath Date: Fri, 21 Feb 2020 19:52:07 -0500 Subject: [PATCH] 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 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Link: https://lkml.kernel.org/r/20200222005213.3873-4-thara.gopinath@linaro.org --- drivers/base/arch_topology.c | 11 +++++++++++ include/linux/arch_topology.h | 10 ++++++++++ 2 files changed, 21 insertions(+) diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c index 6119e11..68dfa49 100644 --- a/drivers/base/arch_topology.c +++ b/drivers/base/arch_topology.c @@ -42,6 +42,17 @@ void topology_set_cpu_scale(unsigned int cpu, unsigned long capacity) per_cpu(cpu_scale, cpu) = capacity; } +DEFINE_PER_CPU(unsigned long, thermal_pressure); + +void arch_set_thermal_pressure(struct cpumask *cpus, + unsigned long th_pressure) +{ + int cpu; + + for_each_cpu(cpu, cpus) + WRITE_ONCE(per_cpu(thermal_pressure, cpu), th_pressure); +} + static ssize_t cpu_capacity_show(struct device *dev, struct device_attribute *attr, char *buf) diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h index 3015ecb..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; -- 2.7.4