linux-kernel - [PATCH v2] sched/Documentation: Add RT_RUNTIME

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Date: Fri, 19 Apr 2024 17:04:32 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: <mingo@...nel.org>, <chrubis@...e.cz>, <rostedt@...dmis.org>,
	<bagasdotme@...il.com>, <corbet@....net>
CC: <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Zhang Qiao
	<zhangqiao22@...wei.com>
Subject: [PATCH v2] sched/Documentation: Add RT_RUNTIME_SHARE documentation

RT_RUNTIME_SHARE is an important strategy for rt bandwidth, and
we should document this sched feature.

Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
Improvements-suggested-by: Bagas Sanjaya <bagasdotme@...il.com>
---
 Documentation/scheduler/sched-rt-group.rst | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/scheduler/sched-rt-group.rst
index d685609ed3d7..eea2fc6f068f 100644
--- a/Documentation/scheduler/sched-rt-group.rst
+++ b/Documentation/scheduler/sched-rt-group.rst
@@ -12,6 +12,7 @@ Real-Time group scheduling
      2.1 System-wide settings
      2.2 Default behaviour
      2.3 Basis for grouping tasks
+     2.4 RT_RUNTIME_SHARE sched feature
    3. Future plans
 
 
@@ -146,6 +147,17 @@ For now, this can be simplified to just the following (but see Future plans):
 
    \Sum_{i} runtime_{i} <= global_runtime
 
+2.4 RT_RUNTIME_SHARE sched feature
+----------------------------------
+
+RT_RUNTIME_SHARE allows a cpu to borrow rt-runtime from other cpus if it runs
+out of its own rt-runtime.
+
+With this feature enabled, a rt-task may hit 100% cpu usage and can stall other
+per-cpu tasks like kworkers, as a result, which leads into system hang.
+
+Thus, it is advised to disable this feature by default to avoid aforementioned
+issue unless you know what you're doing.
 
 3. Future plans
 ===============
-- 
2.18.0.huawei.25