Getting MPD to use RT priority 40.

[jer1956]

I posted that there was a bug in the service that meant MPD never goes real time even with a RT kernel. It was closed as they refused to accept the service was the cause of the problem..
To check for real time use
ps -eo pid,pri_bar,ni,comm.
MPD would have a negative pri_bar if it was real time.
There are only two ways to get real time.
A complicated way using chrt after working out the pid.
Or a simple way. Change the service.
Add
CPUSchedulingPolicy=fifo
CPUSchedulingPriority=40
After you reboot , when you run the PS command again you get a pri_bar of -40. You are running MPD as a real time task.
So how many believing they are using RT are if they check?

[MaxKellermann]

As I already said in your bug report at #1450 (comment) : adding CPUSchedularProfile=fifo as you suggested is a very bad idea. Never do that!
Instead of repeating your bad advice, please read the documentation: https://mpd.readthedocs.io/en/stable/user.html#real-time-scheduling

[jer1956]

It isn’t working. MPD is not using real-time according to that information. Whats the point of setting its prlimit to 40 if it’s stuck as a user task using nice?
You are misleading users.

[leigh123linux]

It isn’t working. MPD is not using real-time. What’s the point of setting its prlimit to 40 if it’s stuck as a user task using nice? You are misleading users.

Maybe your distro is broken, mpd works fine on Fedora.

[leigh@mpd ~]$ ps H -q `pidof -s mpd` -o 'pid,tid,cls,rtprio,comm'
    PID     TID CLS RTPRIO COMMAND
    794     794  TS      - mpd
    794     878  TS      - io
    794     879  FF     40 rtio
    794    5769  TS      - player
    794    5770  TS      - decoder:dsf
    794    5771  FF     40 output:D10

[jer1956]

The MPD realt time priority is _ , meaning it’s using nice.
Only the services are real time.
I will try your command to check my system with its updated service.
Your fedora command does not work with Debian
It will take me a bit of time to find the command differences

[leigh123linux]

The MPD realt time priority is _ , meaning it’s using nice. Only the services are real time. I will try your command to check my system with its updated service. Your fedora command does not work with Debian It will take me a bit of time to find the command differences

Did you read the docs?

https://mpd.readthedocs.io/en/latest/user.html?highlight=realtime#realtime

[MaxKellermann]

You are misleading users.

You're just one step away from being banned here for being an a** towards somebody who invests his free time to try to help you.

My theory is that you didn't read the documentation, and didn't check that your system is properly set up to allow unprivileged real-time scheduling.

[jer1956]

if i get the pid seperately your command works
ps H -q 513 -o pid,tid,cls,rtprio,comm
PID TID CLS RTPRIO COMMAND
513 513 FF 40 mpd
513 553 FF 40 io
513 554 FF 40 rtio
513 3541 FF 40 player
513 3542 FF 40 decoder:flac
513 3543 FF 40 iou-wrk-553
513 3544 FF 40 output:My ALSA
513 11951 TS - output:My ALSA

Now that’s what I call running MPD in real time.
And why do you keep editing out posts you don’t like in a discussion?

[leigh123linux]

if i get the pid seperately your command works ps H -q 513 -o pid,tid,cls,rtprio,comm PID TID CLS RTPRIO COMMAND 513 513 FF 40 mpd 513 553 FF 40 io 513 554 FF 40 rtio 513 3541 FF 40 player 513 3542 FF 40 decoder:flac 513 3543 FF 40 iou-wrk-553 513 3544 FF 40 output:My ALSA 513 11951 TS - output:My ALSA

Now that’s what I call running MPD in real time.

So you want the mpd database and everything else not sound related running high priority and possibly degrading sound?

[jer1956]

Then you should stop saying you have a real time setup.
You don’t!
That’s the real misinformation.

[MaxKellermann]

Then you should stop saying you have a real time setup. You don’t!

WTF ... I have a feeling you have no idea what you are talking about. You are making a clown of yourself.

[jer1956]

No….you are an egotist who can’t stand critism.

[MaxKellermann]

Enough is enough. I have just banned @jer1956.

[twojstaryzdomu]

@MaxKellermann Not to rescind an old discussion, just to ask the validity of my setup. I followed your guide but it wasn't enough when the system was under load and additional steps had to be taken to improve real-time audio.

I understand the problem when everything runs real-time but what about RR class and PTPRIO=50?

# cat /etc/systemd/system/mpd.service.d/10_scheduling.conf 
[Service]
CPUSchedulingPolicy=rr
CPUSchedulingPriority=50
# ps H -q `pidof -s mpd` -o 'pid,tid,cls,rtprio,comm'
  PID   TID CLS RTPRIO COMMAND
20923 20923  RR     50 mpd
20923 20929  RR     50 io
20923 20930  FF     40 rtio
20923 20931  RR     50 player
20923 20932  RR     50 decoder:flac
20923 20952  FF     40 output:Pulseaud
20923 20953  TS      - threaded-ml

It works in combination with pulseaudio (spawned system-wide to secure shared memory but as user mpd), some additional details below. Note RTPRIO=51, one notch higher than mpd.

# cat /etc/systemd/system/pulseaudio.service.d/10_scheduling.conf 
[Service]
ExecStartPost=chrt -p 51 ${MAINPID}
IOSchedulingPriority=1
IOSchedulingClass=realtime
# ps H -q `pidof -s pulseaudio` -o 'pid,tid,cls,rtprio,comm'
  PID   TID CLS RTPRIO COMMAND
  919   919  RR     51 pulseaudio
  919   927  RR     99 alsa-sink-USB A
# grep Limit /etc/systemd/system/pulseaudio.service
LimitRTPRIO=99
LimitRTTIME=infinity
LimitNICE=-20
LimitMEMLOCK=infinity
# cat /etc/pulse/daemon.conf
cpu-limit = no
high-priority = yes
nice-level = -12
rlimit-nice = -12
realtime-scheduling = yes
realtime-priority = 99
rlimit-rtprio = 99
exit-idle-time = -1
default-sample-format = s24le
default-sample-rate = 96000
resample-method = soxr-mq
enable-shm = yes

This setup goes back a few years, IOSchedulingPriority as I recall helped resolve skipping when under heavy load. The environment with the above setup has meagre resources.