From plain Debian + Jack2 + MPD to Moode: doubts

[Tim Curtis]

The 64-bit kernel already has preempt-rt applied.

Thanks for pointing this out.
So the 64-bit image is enabled for real-time/low-latency out-of-the-box, is it?
Are there processes using the real-time scheduling policy in Moode per your knowledge?

Not preempt-rt but preempt.

Below are the preempt related compile options that are used for 32 and 64 bit raspberry pi kernels.

The 32 bit kernels are compiled with CONFIG_PREEMPT_VOLUNTARY=y

Code:

pi@rp3:~ $ uname -a
Linux rp3 5.4.49-v7+ #1323 SMP Fri Jun 26 14:34:26 BST 2020 armv7l GNU/Linux
pi@rp3:~ $ sudo modprobe configs
pi@rp3:~ $ zcat /proc/config.gz | grep PREEMPT
# CONFIG_PREEMPT_NONE is not set
CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set
CONFIG_PREEMPTIRQ_TRACEPOINTS=y
# CONFIG_PREEMPTIRQ_EVENTS is not set
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set

The 64-bit kernels are compiled with CONFIG_PREEMPT=y

Code:

pi@rp3:~ $ uname -a
Linux rp3 5.4.49-v8+ #1323 SMP PREEMPT Fri Jun 26 14:47:11 BST 2020 aarch64 GNU/Linux
pi@rp3:~ $ sudo modprobe configs
pi@rp3:~ $ zcat /proc/config.gz | grep PREEMPT
# CONFIG_PREEMPT_NONE is not set
# CONFIG_PREEMPT_VOLUNTARY is not set
CONFIG_PREEMPT=y
CONFIG_PREEMPT_COUNT=y
CONFIG_PREEMPTION=y
CONFIG_PREEMPT_RCU=y
CONFIG_PREEMPT_NOTIFIERS=y
CONFIG_DEBUG_PREEMPT=y
CONFIG_PREEMPTIRQ_TRACEPOINTS=y
# CONFIG_PREEMPTIRQ_EVENTS is not set
# CONFIG_PREEMPT_TRACER is not set
# CONFIG_PREEMPTIRQ_DELAY_TEST is not set

Article on Linux kernel preemptive scheduling
https://www.codeblueprint.co.uk/2019/12/...ghput.html

MPD will use "real-time" prioritization and scheduling policies if they are available in the kernel.
https://www.musicpd.org/doc/html/user.ht...scheduling

Below shows CONFIG_RT_GROUP_SCHED is not set (disabled). This is for both 32 and 64-bit kernels.

Code:

pi@rp3:~ $ zcat /proc/config.gz | grep CONFIG_RT_GROUP_SCHED
# CONFIG_RT_GROUP_SCHED is not set
pi@rp3:~ $ zgrep ^CONFIG_RT_GROUP_SCHED /proc/config.gz
pi@rp3:~ $

Process status for MPD showing use of RT scheduler priorities and policies for certain threads

Code:

pi@rp3:~ $ ps H -q `pidof -s mpd` -o 'pid,tid,cls,rtprio,comm'
 PID   TID CLS RTPRIO COMMAND
1216  1216  TS      - mpd
1216  1220  TS      - io
1216  1221  FF     50 rtio
1216  1442  TS      - player
1216  1443  TS      - decoder:faad
1216  1485  FF     50 output:ALSA def