From: Artem Bityutskiy Date: Mon, 17 Mar 2025 13:55:40 +0000 (+0200) Subject: Documentation: admin-guide: pm: Document intel_idle C1 demotion X-Git-Tag: v6.16-rc1~109^2^2~4 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=af3a1b6a18258168f09e4ebc014b368bb0e845b0;p=linux-block.git 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 Link: https://patch.msgid.link/20250317135541.1471754-3-dedekind1@gmail.com Signed-off-by: Rafael J. Wysocki --- diff --git a/Documentation/admin-guide/pm/intel_idle.rst b/Documentation/admin-guide/pm/intel_idle.rst index 5940528146eb..ed6f055d4b14 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/``: + +``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: