Message-ID: <af62f3301bea0b7c17c777002bc2e63ba705dd30.camel@linux.intel.com>
Date: Fri, 14 Nov 2025 10:32:45 -0800
From: srinivas pandruvada <srinivas.pandruvada@...ux.intel.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: daniel.lezcano@...aro.org, corbet@....net, linux-pm@...r.kernel.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 rdunlap@...radead.org
Subject: Re: [PATCH v2] Documentation: thermal: Add documentation for
 thermal throttle

On Fri, 2025-11-14 at 17:27 +0100, Rafael J. Wysocki wrote:
> On Thu, Nov 13, 2025 at 10:21 PM Srinivas Pandruvada
> <srinivas.pandruvada@...ux.intel.com> wrote:
> > 
> > Add documentation for Intel thermal throttling reporting events.
> > 
> > Signed-off-by: Srinivas Pandruvada
> > <srinivas.pandruvada@...ux.intel.com>
> > ---
> > 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@...ux.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.
> > +
> > --
> 
> Applied as 6.19 material with some adjustments:
> - The new file name is intel_thermal_throttle.rst
> - The subject has been edited to mention Intel
> - There are some minor edits in the document
> 
> Please check in the bleeding-edge branch if it still looks good.

Looks good.

Thanks,
Srinivas

> 
> Thanks!

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