Re: [Patch v2 2/2] ACPI: processor: reduce CPUFREQ thermal reduction pctg for Tegra241

Sumit Gupta
2023-10-06T15:15:20Z

On 04/10/23 01:07, Rafael J. Wysocki wrote:
> External email: Use caution opening links or attachments
>
>
> On Wed, Sep 13, 2023 at 6:47 PM Sumit Gupta <sumitg@nvidia.com> wrote:
>>
>> From: Srikar Srimath Tirumala <srikars@nvidia.com>
>>
>> Current implementation of processor_thermal performs software throttling
>> in fixed steps of "20%" which can be too coarse for some platforms.
>> We observed some performance gain after reducing the throttle percentage.
>> Change the CPUFREQ thermal reduction percentage and maximum thermal steps
>> to be configurable. Also, update the default values of both for Nvidia
>> Tegra241 (Grace) SoC. The thermal reduction percentage is reduced to "5%"
>> and accordingly the maximum number of thermal steps are increased as they
>> are derived from the reduction percentage.
>>
>> Signed-off-by: Srikar Srimath Tirumala <srikars@nvidia.com>
>> Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
>> ---
>> drivers/acpi/processor_thermal.c | 41 +++++++++++++++++++++++++++++---
>> 1 file changed, 38 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/acpi/processor_thermal.c b/drivers/acpi/processor_thermal.c
>> index b7c6287eccca..30f2801abce6 100644
>> --- a/drivers/acpi/processor_thermal.c
>> +++ b/drivers/acpi/processor_thermal.c
>> @@ -26,7 +26,16 @@
>> */
>>
>> #define CPUFREQ_THERMAL_MIN_STEP 0
>> -#define CPUFREQ_THERMAL_MAX_STEP 3
>> +
>> +static int cpufreq_thermal_max_step = 3;
>
> __read_mostly I suppose?
>

Added in v3.

>> +
>> +/*
>> + * Minimum throttle percentage for processor_thermal cooling device.
>
> + *
>
>> + * The processor_thermal driver uses it to calculate the percentage amount by
>> + * which cpu frequency must be reduced for each cooling state. This is also used
>> + * to calculate the maximum number of throttling steps or cooling states.
>> + */
>> +static int cpufreq_thermal_pctg = 20;
>
> __read_mostly here too?
>

Added in v3.

>>
>> static DEFINE_PER_CPU(unsigned int, cpufreq_thermal_reduction_pctg);
>>
>> @@ -71,7 +80,7 @@ static int cpufreq_get_max_state(unsigned int cpu)
>> if (!cpu_has_cpufreq(cpu))
>> return 0;
>>
>> - return CPUFREQ_THERMAL_MAX_STEP;
>> + return cpufreq_thermal_max_step;
>> }
>>
>> static int cpufreq_get_cur_state(unsigned int cpu)
>> @@ -113,7 +122,8 @@ static int cpufreq_set_cur_state(unsigned int cpu, int state)
>> if (!policy)
>> return -EINVAL;
>>
>> - max_freq = (policy->cpuinfo.max_freq * (100 - reduction_pctg(i) * 20)) / 100;
>> + max_freq = (policy->cpuinfo.max_freq *
>> + (100 - reduction_pctg(i) * cpufreq_thermal_pctg)) / 100;
>>
>> cpufreq_cpu_put(policy);
>>
>> @@ -126,10 +136,35 @@ static int cpufreq_set_cur_state(unsigned int cpu, int state)
>> return 0;
>> }
>>
>
> #ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>
>> +#define SMCCC_SOC_ID_T241 0x036b0241
>> +
>> +void acpi_thermal_cpufreq_config_nvidia(void)
>
> static void ?
>

Added in v3.

>> +{
>> +#ifdef CONFIG_HAVE_ARM_SMCCC_DISCOVERY
>> + s32 soc_id = arm_smccc_get_soc_id_version();
>> +
>> + /* Check JEP106 code for NVIDIA Tegra241 chip (036b:0241) */
>> + if ((soc_id < 0) || (soc_id != SMCCC_SOC_ID_T241))
>
> Inner parens are redundant.
>

Removed in v3.

>> + return;
>> +
>> + /* Reduce the CPUFREQ Thermal reduction percentage to 5% */
>> + cpufreq_thermal_pctg = 5;
>> +
>> + /*
>> + * Derive the MAX_STEP from minimum throttle percentage so that the reduction
>> + * percentage doesn't end up becoming negative. Also, cap the MAX_STEP so that
>> + * the CPU performance doesn't become 0.
>> + */
>> + cpufreq_thermal_max_step = ((100 / cpufreq_thermal_pctg) - 1);
>
> Outer parens are redundant.
>

ACK.

>> +#endif
>> +}
>
> #else
> static inline void void acpi_thermal_cpufreq_config_nvidia(void) {}
> #endif
>
>> +
>> void acpi_thermal_cpufreq_init(struct cpufreq_policy *policy)
>> {
>> unsigned int cpu;
>>
>> + acpi_thermal_cpufreq_config_nvidia();
>> +
>> for_each_cpu(cpu, policy->related_cpus) {
>> struct acpi_processor *pr = per_cpu(processors, cpu);
>> int ret;
>> --
>
> And patch [1/2] needs to be rebased on the current ACPI thermal
> material in linux-next.
>

Ok.

> Thanks!