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thread/Util: lower the real-time priority from 50 to 40 

On linux-rt, kernel IRQ threads are configured with priority=50, and
this change configures MPD somewhat below that priority, leaving some
room for other programs to be configured in between.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/643
This commit is contained in:
Max Kellermann 2019-10-09 14:40:02 +02:00
parent 2f3e94f8d0
commit c89c7f71a2
5 changed files with 10 additions and 9 deletions
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1
NEWS
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@ -28,6 +28,7 @@ ver 0.22 (not yet released)
- jack: add option "auto_destination_ports" - jack: add option "auto_destination_ports"
- jack: report error details - jack: report error details
- pulse: add option "media_role" - pulse: add option "media_role"
* lower the real-time priority from 50 to 40
* switch to C++17 * switch to C++17
- GCC 7 or clang 4 (or newer) recommended - GCC 7 or clang 4 (or newer) recommended

8
doc/user.rst
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@ -804,13 +804,13 @@ This is only possible you allow :program:`MPD` to do it. This privilege is contr
.. code-block:: none .. code-block:: none
ulimit -HS -r 50; mpd ulimit -HS -r 40; mpd
Or you can use the :command:`prlimit` program from the util-linux package: Or you can use the :command:`prlimit` program from the util-linux package:
.. code-block:: none .. code-block:: none
prlimit --rtprio=50 --rttime=unlimited mpd prlimit --rtprio=40 --rttime=unlimited mpd
The systemd service file shipped with :program:`MPD` comes with this setting. The systemd service file shipped with :program:`MPD` comes with this setting.
@ -828,10 +828,10 @@ You can verify whether the real-time scheduler is active with the ps command:
PID TID CLS RTPRIO COMMAND PID TID CLS RTPRIO COMMAND
16257 16257 TS - mpd 16257 16257 TS - mpd
16257 16258 TS - io 16257 16258 TS - io
16257 16259 FF 50 rtio 16257 16259 FF 40 rtio
16257 16260 TS - player 16257 16260 TS - player
16257 16261 TS - decoder 16257 16261 TS - decoder
16257 16262 FF 50 output:ALSA 16257 16262 FF 40 output:ALSA
16257 16263 IDL 0 update 16257 16263 IDL 0 update
The CLS column shows the CPU scheduler; TS is the normal scheduler; FF and RR are real-time schedulers. In this example, two threads use the real-time scheduler: the output thread and the rtio (real-time I/O) thread; these two are the important ones. The database update thread uses the idle scheduler ("IDL in ps), which only gets CPU when no other process needs it. The CLS column shows the CPU scheduler; TS is the normal scheduler; FF and RR are real-time schedulers. In this example, two threads use the real-time scheduler: the output thread and the rtio (real-time I/O) thread; these two are the important ones. The database update thread uses the idle scheduler ("IDL in ps), which only gets CPU when no other process needs it.

2
src/thread/Util.cxx
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@ -101,7 +101,7 @@ SetThreadRealtime()
{ {
#ifdef __linux__ #ifdef __linux__
struct sched_param sched_param; struct sched_param sched_param;
sched_param.sched_priority = 50; sched_param.sched_priority = 40;
int policy = SCHED_FIFO; int policy = SCHED_FIFO;
#ifdef SCHED_RESET_ON_FORK #ifdef SCHED_RESET_ON_FORK

4
systemd/system/mpd.service.in
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@ -12,8 +12,8 @@ ExecStart=@prefix@/bin/mpd --no-daemon
# periodic wakeups which are unnecessary if MPD is not playing. # periodic wakeups which are unnecessary if MPD is not playing.
#WatchdogSec=120 #WatchdogSec=120
# allow MPD to use real-time priority 50 # allow MPD to use real-time priority 40
LimitRTPRIO=50 LimitRTPRIO=40
LimitRTTIME=infinity LimitRTTIME=infinity
# disallow writing to /usr, /bin, /sbin, ... # disallow writing to /usr, /bin, /sbin, ...

4
systemd/user/mpd.service.in
View File

@ -12,8 +12,8 @@ ExecStart=@prefix@/bin/mpd --no-daemon
# periodic wakeups which are unnecessary if MPD is not playing. # periodic wakeups which are unnecessary if MPD is not playing.
#WatchdogSec=120 #WatchdogSec=120
# allow MPD to use real-time priority 50 # allow MPD to use real-time priority 40
LimitRTPRIO=50 LimitRTPRIO=40
LimitRTTIME=infinity LimitRTTIME=infinity
# disallow writing to /usr, /bin, /sbin, ... # disallow writing to /usr, /bin, /sbin, ...