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SubjectRe: [Patch v9 3/8] arm,arm64,drivers:Add infrastructure to store and update instantaneous thermal pressure
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On 02/13/2020 07:25 AM, Amit Kucheria wrote:
> 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.

I will fix this
>
>>
>> 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.

No reason. No reason not to as well as arch_topology is "Arm specific
cpu topology file" and changes are one-liners.

>
>> 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>
>


--
Warm Regards
Thara

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