From 6586705bc2dc06908309bf65d79efa53a347c9f0 Mon Sep 17 00:00:00 2001 From: Tao Cui Date: Mon, 24 Aug 2026 21:21:16 +0800 Subject: [PATCH] docs/sched_ext: document that cgroup CPU knobs are scheduler-dependent The scheduler core communicates the initial cpu controller settings to the BPF scheduler through ops.cgroup_init() and reports subsequent changes through the corresponding ops.cgroup_set_*() callbacks. Whether and how a knob takes effect is up to the loaded scheduler: it may implement the corresponding callback partially or not at all, so cpu.max, cpu.weight and friends can silently have no effect. Document this in the basics section of sched-ext.rst. Signed-off-by: Tao Cui Reviewed-by: Andrea Righi Signed-off-by: Tejun Heo --- Documentation/scheduler/sched-ext.rst | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/Documentation/scheduler/sched-ext.rst b/Documentation/scheduler/sched-ext.rst index 35b550671ca7..794ae80b3ba3 100644 --- a/Documentation/scheduler/sched-ext.rst +++ b/Documentation/scheduler/sched-ext.rst @@ -242,6 +242,21 @@ optional. The following modified excerpt is from .name = "simple", }; +Scheduler-Dependent Knobs +------------------------- + +The fair-class scheduler enforces CPU controller settings such as +``cpu.max``, ``cpu.weight`` and ``cpu.idle``. For sched_ext tasks, the +scheduler core communicates these settings to the BPF scheduler +through ``ops.cgroup_init()`` and reports subsequent changes through +the corresponding ``ops.cgroup_set_*()`` callbacks. Similarly, per-task +nice changes are converted to weights and reported through +``ops.set_weight()``. + +Each BPF scheduler is responsible for implementing the scheduling +semantics of these settings and may choose to ignore them. Consult the +loaded scheduler's documentation before relying on these controls. + Dispatch Queues ---------------