linux-kernel - [PATCH] sched/deadline: document behavior of sched

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Message-Id: <1473365399-29430-1-git-send-email-tommaso.cucinotta@sssup.it>
Date:   Thu,  8 Sep 2016 22:09:59 +0200
From:   Tommaso Cucinotta <tommaso.cucinotta@...up.it>
To:     Luca Abeni <luca.abeni@...tn.it>,
        Juri Lelli <juri.lelli@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-dl@...is.sssup.it,
        Tommaso Cucinotta <tommaso.cucinotta@...up.it>
Subject: [PATCH] sched/deadline: document behavior of sched_yield()

This is a documentation only patch, explaining the
behavior of sched_yield() when a SCHED_DEADLINE
task calls it (give up remaining runtime and
suspend till next period).
---
 Documentation/scheduler/sched-deadline.txt | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/Documentation/scheduler/sched-deadline.txt b/Documentation/scheduler/sched-deadline.txt
index 53a2fe1..cb43421 100644
--- a/Documentation/scheduler/sched-deadline.txt
+++ b/Documentation/scheduler/sched-deadline.txt
@@ -16,6 +16,7 @@ CONTENTS
    4.1 System-wide settings
    4.2 Task interface
    4.3 Default behavior
+   4.4 Behavior of sched_yield()
  5. Tasks CPU affinity
    5.1 SCHED_DEADLINE and cpusets HOWTO
  6. Future plans
@@ -426,6 +427,18 @@ CONTENTS
  Finally, notice that in order not to jeopardize the admission control a
  -deadline task cannot fork.
 
+4.4 Behavior of sched_yield()
+-----------------------------
+
+ When a SCHED_DEADLINE task calls sched_yield(), it gives up its
+ remaining runtime and is suspended till the next reservation period,
+ when its runtime will be replenished.  This allows the task to
+ wake-up exactly at the beginning of the next period. Also, this may
+ be useful in the future with bandwidth reclaiming mechanisms, where
+ sched_yield() will make the leftoever runtime available for
+ reclamation by other SCHED_DEADLINE tasks.
+
+
 5. Tasks CPU affinity
 =====================
 
-- 
2.7.4