From f901cd042bb7872cc097c6c2d846b70b022ba3f0 Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@duempel.org>
Date: Tue, 27 Oct 2015 10:31:50 +0100
Subject: doc/user: section about real-time scheduling
---
doc/user.xml | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 52 insertions(+)
diff --git a/doc/user.xml b/doc/user.xml
index d1c7ff595..010d2f980 100644
--- a/doc/user.xml
+++ b/doc/user.xml
@@ -1190,6 +1190,58 @@ database {
plugin).
</para>
</section>
+
+ <section id="realtime">
+ <title>Real-Time Scheduling</title>
+
+ <para>
+ On Linux, <application>MPD</application> attempts to configure
+ <ulink
+ url="https://en.wikipedia.org/wiki/Real-time_computing">real-time
+ scheduling</ulink> for some threads that benefit from it.
+ </para>
+
+ <para>
+ This is only possible you allow <application>MPD</application>
+ to do it. This privilege is controlled by
+ <varname>RLIMIT_RTPRIO</varname>
+ <varname>RLIMIT_RTTIME</varname>. You can configure this
+ privilege with <command>ulimit</command> before launching
+ <application>MPD</application>:
+ </para>
+
+ <programlisting>ulimit -HS -r 50; mpd</programlisting>
+
+ <para>
+ Or you can use the <command>prlimit</command> program from the
+ <application>util-linux</application> package:
+ </para>
+
+ <programlisting>prlimit --rtprio=50 --rttime=unlimited mpd</programlisting>
+
+ <para>
+ The <application>systemd</application> service file shipped
+ with <application>MPD</application> comes with this setting.
+ </para>
+
+ <para>
+ This works only if the Linux kernel was compiled with
+ <varname>CONFIG_RT_GROUP_SCHED</varname> disabled. Use the
+ following command to check this option for your current
+ kernel:
+ </para>
+
+ <programlisting>zgrep ^CONFIG_RT_GROUP_SCHED /proc/config.gz</programlisting>
+
+ <note>
+ <para>
+ There is a rumor that real-time scheduling improves audio
+ quality. That is not true. All it does is reduce the
+ probability of skipping (audio buffer xruns) when the
+ computer is under heavy load.
+ </para>
+ </note>
+ </section>
</chapter>
<chapter id="use">
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