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Documentation: admin-guide: pm: Document intel_idle C1 demotion 

Document the intel_idle driver sysfs file for enabling/disabling C1
demotion.

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Link: https://patch.msgid.link/20250317135541.1471754-3-dedekind1@gmail.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
pull/1250/head
Artem Bityutskiy 2025-03-17 15:55:40 +02:00 committed by Rafael J. Wysocki
parent 6138f34515
commit af3a1b6a18
1 changed files with 21 additions and 0 deletions
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Documentation/admin-guide/pm/intel_idle.rst
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@ -38,6 +38,27 @@ instruction at all.
only way to pass early-configuration-time parameters to it is via the kernel
command line.
Sysfs Interface
===============
The ``intel_idle`` driver exposes the following ``sysfs`` attributes in
``/sys/devices/system/cpu/cpuidle/``:
``intel_c1_demotion``
Enable or disable C1 demotion for all CPUs in the system. This file is
only exposed on platforms that support the C1 demotion feature and where
it was tested. Value 0 means that C1 demotion is disabled, value 1 means
that it is enabled. Write 0 or 1 to disable or enable C1 demotion for
all CPUs.
The C1 demotion feature involves the platform firmware demoting deep
C-state requests from the OS (e.g., C6 requests) to C1. The idea is that
firmware monitors CPU wake-up rate, and if it is higher than a
platform-specific threshold, the firmware demotes deep C-state requests
to C1. For example, Linux requests C6, but firmware noticed too many
wake-ups per second, and it keeps the CPU in C1. When the CPU stays in
C1 long enough, the platform promotes it back to C6. This may improve
some workloads' performance, but it may also increase power consumption.
.. _intel-idle-enumeration-of-states: