Re: [PATCH v2] Documentation: thermal: Add documentation for thermal throttle

[Randy Dunlap <rdunlap@infradead.org>]

On 11/13/25 1:21 PM, Srinivas Pandruvada wrote:
> Add documentation for Intel thermal throttling reporting events.
> 
> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>

Tested-by: Randy Dunlap <rdunlap@infradead.org>

> ---
> v2:
>  - Addressed comments from Rafael
>  - Limit line lengths ~80 columns
> 
>  Documentation/admin-guide/thermal/index.rst   |  1 +
>  .../admin-guide/thermal/thermal_throttle.rst  | 92 +++++++++++++++++++
>  2 files changed, 93 insertions(+)
>  create mode 100644 Documentation/admin-guide/thermal/thermal_throttle.rst
> 
> diff --git a/Documentation/admin-guide/thermal/index.rst b/Documentation/admin-guide/thermal/index.rst
> index 193b7b01a87d..2e0cafd19f6b 100644
> --- a/Documentation/admin-guide/thermal/index.rst
> +++ b/Documentation/admin-guide/thermal/index.rst
> @@ -6,3 +6,4 @@ Thermal Subsystem
>     :maxdepth: 1
>  
>     intel_powerclamp
> +   thermal_throttle
> diff --git a/Documentation/admin-guide/thermal/thermal_throttle.rst b/Documentation/admin-guide/thermal/thermal_throttle.rst
> new file mode 100644
> index 000000000000..cac2bc3176ce
> --- /dev/null
> +++ b/Documentation/admin-guide/thermal/thermal_throttle.rst
> @@ -0,0 +1,92 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +.. include:: <isonum.txt>
> +
> +=======================================
> +Intel thermal throttle events reporting
> +=======================================
> +
> +:Author: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
> +
> +Introduction
> +------------
> +
> +Intel processors have built in automatic and adaptive thermal monitoring
> +mechanisms that force the processor to reduce its power consumption in order
> +to operate within predetermined temperature limits.
> +
> +Refer to section "THERMAL MONITORING AND PROTECTION" in the "Intel® 64 and
> +IA-32 Architectures Software Developer’s Manual Volume 3 (3A, 3B, 3C, & 3D):
> +System Programming Guide" for more details.
> +
> +In general, there are two mechanisms to control the core temperature of the
> +processor. They are called "Thermal Monitor 1 (TM1) and Thermal Monitor 2 (TM2)".
> +
> +The status of the temperature sensor that triggers the thermal monitor (TM1/TM2)
> +is indicated through the "thermal status flag" and "thermal status log flag" in
> +the MSR_IA32_THERM_STATUS for core level and MSR_IA32_PACKAGE_THERM_STATUS for
> +package level.
> +
> +Thermal Status flag, bit 0 — When set, indicates that the processor core
> +temperature is currently at the trip temperature of the thermal monitor and that
> +the processor power consumption is being reduced via either TM1 or TM2, depending
> +on which is enabled. When clear, the flag indicates that the core temperature is
> +below the thermal monitor trip temperature. This flag is read only.
> +
> +Thermal Status Log flag, bit 1 — When set, indicates that the thermal sensor has
> +tripped since the last power-up or reset or since the last time that software
> +cleared this flag. This flag is a sticky bit; once set it remains set until
> +cleared by software or until a power-up or reset of the processor. The default
> +state is clear.
> +
> +It is possible that when user reads MSR_IA32_THERM_STATUS or
> +MSR_IA32_PACKAGE_THERM_STATUS, TM1/TM2 is not active. In this case,
> +"Thermal Status flag" will read "0" and the "Thermal Status Log flag" will be set
> +to show any previous "TM1/TM2" activation. But since it needs to be cleared by
> +the software, it can't show the number of occurrences of "TM1/TM2" activations.
> +
> +Hence, Linux provides counters of how many times the "Thermal Status flag" was
> +set. Also presents how long the "Thermal Status flag" was active in milliseconds.
> +Using these counters, users can check if the performance was limited because of
> +thermal events. It is recommended to read from sysfs instead of directly reading
> +MSRs as the "Thermal Status Log flag" is reset by the driver to implement rate
> +control.
> +
> +Sysfs Interface
> +---------------
> +
> +Thermal throttling events are presented for each CPU under
> +"/sys/devices/system/cpu/cpuX/thermal_throttle/", where "X" is the CPU number.
> +
> +All these counters are read-only. They can't be reset to 0. So, they can potentially
> +overflow after reaching the maximum 64 bit unsigned integer.
> +
> +``core_throttle_count``
> +	This shows number of times "Thermal Status flag" changed from 0 to 1 for this
> +	CPU since OS boot and thermal vector is initialized. This is a 64 bit counter.
> +
> +``package_throttle_count``
> +	This shows number of times "Thermal Status flag" changed from 0 to 1 for the
> +	package containing this CPU since OS boot and thermal vector is initialized.
> +	Package status is broadcast to all CPUs; all CPUs in the package increment
> +	this count. This is a 64-bit counter.
> +
> +``core_throttle_max_time_ms``
> +	This shows the maximum amount of time for which "Thermal Status flag"
> +	has been set to 1 for this CPU at the core level since OS boot and thermal
> +	vector is initialized.
> +
> +``package_throttle_max_time_ms``
> +	This shows the maximum amount of time for which "Thermal Status flag"
> +	has been set to 1 for the package containing this CPU since OS boot and
> +	thermal vector is initialized.
> +
> +``core_throttle_total_time_ms``
> +	This shows the cumulative time for which "Thermal Status flag" has been
> +	set to 1 for this CPU for core level since OS boot and thermal vector
> +	is initialized.
> +
> +``package_throttle_total_time_ms``
> +	This shows the cumulative time for which "Thermal Status flag" has been set
> +	to 1 for the package containing this CPU since OS boot and thermal vector is
> +	initialized.
> +

-- 
~Randy