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SubjectRe: [Patch v9 3/8] arm,arm64,drivers:Add infrastructure to store and update instantaneous thermal pressure
On Wed, Jan 29, 2020 at 4:06 AM Thara Gopinath
<thara.gopinath@linaro.org> wrote:
>
> 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.

s/capped/decreased to have consistent use throughout the series e.g. in patch 1.

Though personally, I like "capped capacity" in which case
s/decreased/capped in patch 1 and elsewhere.

>
> topology_get_thermal_pressure can be hooked into the scheduler specified
> arch_cpu_thermal_capacity 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 upto 1 tick period.
>
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> ---
>
> v6->v7:
> - Changed the input argument in arch_set_thermal_pressure from
> capped capacity to delta capacity(thermal pressure) as per
> Ionela's review comments.
>
> arch/arm/include/asm/topology.h | 3 +++
> arch/arm64/include/asm/topology.h | 3 +++

Any particular reason to enable this for arm/arm64 in this patch
itself? I'd have enabled them in two separate patches after this one.

> drivers/base/arch_topology.c | 11 +++++++++++
> include/linux/arch_topology.h | 10 ++++++++++
> 4 files changed, 27 insertions(+)
>
> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
> index 8a0fae9..3a50a19 100644
> --- a/arch/arm/include/asm/topology.h
> +++ b/arch/arm/include/asm/topology.h
> @@ -16,6 +16,9 @@
> /* Enable topology flag updates */
> #define arch_update_cpu_topology topology_update_cpu_topology
>
> +/* Replace task scheduler's default thermal pressure retrieve API */
> +#define arch_cpu_thermal_pressure topology_get_thermal_pressure
> +
> #else
>
> static inline void init_cpu_topology(void) { }
> diff --git a/arch/arm64/include/asm/topology.h b/arch/arm64/include/asm/topology.h
> index a4d945d..a70896f 100644
> --- a/arch/arm64/include/asm/topology.h
> +++ b/arch/arm64/include/asm/topology.h
> @@ -25,6 +25,9 @@ int pcibus_to_node(struct pci_bus *bus);
> /* Enable topology flag updates */
> #define arch_update_cpu_topology topology_update_cpu_topology
>
> +/* Replace task scheduler's default thermal pressure retrieve API */
> +#define arch_cpu_thermal_pressure topology_get_thermal_pressure
> +
> #include <asm-generic/topology.h>
>
> #endif /* _ASM_ARM_TOPOLOGY_H */
> 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;

<snip>

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