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Message-ID: <63eea3ac-4714-2c54-c740-84f9f9e7fd64@nvidia.com>
Date: Mon, 21 Aug 2023 18:54:08 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
CC: <rui.zhang@...el.com>, <lenb@...nel.org>, <treding@...dia.com>,
<jonathanh@...dia.com>, <linux-acpi@...r.kernel.org>,
<linux-kernel@...r.kernel.org>, <sanjayc@...dia.com>,
<ksitaraman@...dia.com>, <srikars@...dia.com>,
<jbrasen@...dia.com>, <bbasu@...dia.com>,
Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch 2/2] ACPI: processor: Add support to configure CPUFREQ
reduction pctg
On 19/08/23 00:10, Rafael J. Wysocki wrote:
> External email: Use caution opening links or attachments
>
>
> On Thu, Aug 17, 2023 at 11:31 AM Sumit Gupta <sumitg@...dia.com> wrote:
>>
>> From: Srikar Srimath Tirumala <srikars@...dia.com>
>>
>> Add support to configure the CPUFREQ reduction percentage and set the
>> maximum number of throttling steps accordingly. Current implementation
>> of processor_thermal performs software throttling in fixed steps of
>> "20%" which can be too coarse for some platforms. Change that by adding
>> new config to provide the reduction percentage.
>>
>> Signed-off-by: Srikar Srimath Tirumala <srikars@...dia.com>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> ---
>> drivers/acpi/Kconfig | 15 +++++++++++++++
>> drivers/acpi/processor_thermal.c | 19 ++++++++++++++++---
>> 2 files changed, 31 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
>> index 00dd309b6682..287cf58defbf 100644
>> --- a/drivers/acpi/Kconfig
>> +++ b/drivers/acpi/Kconfig
>> @@ -254,6 +254,21 @@ config ACPI_DOCK
>> config ACPI_CPU_FREQ_PSS
>> bool
>>
>> +config ACPI_CPU_FREQ_THERM_HAS_PARAMS
>> + bool "CPU frequency throttling control"
>> + depends on ACPI_PROCESSOR
>> +
>> +config ACPI_CPU_FREQ_THERM_MIN_THROT_PCTG
>> + int "Minimum throttle percentage for processor_thermal cooling device"
>> + depends on ACPI_CPU_FREQ_THERM_HAS_PARAMS
>> + default 20
>> + help
>> + The processor_thermal driver uses this config to calculate the
>> + percentage amount by which cpu frequency must be reduced for each
>> + cooling state. The config is also used to calculate the maximum number
>> + of throttling steps or cooling states supported by the driver. Value
>> + must be an unsigned integer in the range [1, 50].
>> +
>
> I don't think that the new Kconfig symbols are particularly useful.
> At least they don't help the distro vendors that each would need to
> pick up a specific value for their kernel anyway.
>
> I also wonder how the users building their own kernels are supposed to
> determine the values suitable for the target systems.
>
We observed some perf gain after reducing the throttle percentage.
Currently, kept the default to '20%' as before.
Based on need, a vendor can overwrite the default value with macro
'CONFIG_ACPI_CPU_FREQ_THERM_MIN_THROT_PCTG'. Otherwise, the behavior
will remain same.
Thank you,
Sumit Gupta
>> config ACPI_PROCESSOR_CSTATE
>> def_bool y
>> depends on ACPI_PROCESSOR
>> diff --git a/drivers/acpi/processor_thermal.c b/drivers/acpi/processor_thermal.c
>> index b7c6287eccca..ee443cc69b73 100644
>> --- a/drivers/acpi/processor_thermal.c
>> +++ b/drivers/acpi/processor_thermal.c
>> @@ -25,8 +25,20 @@
>> * _any_ cpufreq driver and not only the acpi-cpufreq driver.
>> */
>>
>> -#define CPUFREQ_THERMAL_MIN_STEP 0
>> -#define CPUFREQ_THERMAL_MAX_STEP 3
>> +#define CPUFREQ_THERMAL_MIN_STEP 0
>> +#ifdef CONFIG_ACPI_CPU_FREQ_THERM_HAS_PARAMS
>> +#define CPUFREQ_THERMAL_PCTG CONFIG_ACPI_CPU_FREQ_THERM_MIN_THROT_PCTG
>> +
>> +/* Derive the MAX_STEP from minimum throttle percentage so that the reduction
>> + * percentage does end up becoming negative. Also cap the MAX_STEP so that
>> + * the CPU performance doesn't become 0.
>> + */
>> +#define CPUFREQ_THERMAL_MAX_STEP ((100 / CPUFREQ_THERMAL_PCTG) - 1)
>> +
>> +#else
>> +#define CPUFREQ_THERMAL_MAX_STEP 3
>> +#define CPUFREQ_THERMAL_PCTG 20
>> +#endif
>>
>> static DEFINE_PER_CPU(unsigned int, cpufreq_thermal_reduction_pctg);
>>
>> @@ -113,7 +125,8 @@ 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);
>>
>> --
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