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

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Message-ID: <20240131123238.2332064-1-zhangqiao22@huawei.com>
Date: Wed, 31 Jan 2024 20:32:38 +0800
From: Zhang Qiao <zhangqiao22@...wei.com>
To: <corbet@....net>
CC: <mingo@...nel.org>, <chrubis@...e.cz>, <zhangqiao22@...wei.com>,
	<linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] 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>
---
 Documentation/scheduler/sched-rt-group.rst | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/Documentation/scheduler/sched-rt-group.rst b/Documentation/scheduler/sched-rt-group.rst
index d685609ed3d7..4d8eceb71f5e 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 +147,16 @@ 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 borrows rt-runtime from other cpus if it runs
+out of its own rt-runtime.
+
+With this feature enabled, a rt-task probably hits 100% cpu usage and starves
+per-cpu tasks like kworkers, as a result, it may hang up the whole system.
+Therefore, in order to avoid such exception, recommand to disable this feature
+by default unless you really know what you're up to.
 
 3. Future plans
 ===============
-- 
2.18.0.huawei.25