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[2/2] Documentation: admin-guide: pm: document intel_idle C1 demotion

Message ID 20250212084232.2349984-2-dedekind1@gmail.com
State New
Headers show
Series [1/2] intel_idle: Add C1 demotion on/off sysfs knob | expand

Commit Message

Artem Bityutskiy Feb. 12, 2025, 8:42 a.m. UTC 
From: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

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

Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
---
 Documentation/admin-guide/pm/intel_idle.rst | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)
diff mbox series

Patch

diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst
index 39bd6ecce7de..a1daa0fe045a 100644
--- a/Documentation/admin-guide/pm/intel_idle.rst
+++ b/Documentation/admin-guide/pm/intel_idle.rst
@@ -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/``:
+
+``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: