Dedicate CPU core for MPD

[Tim Curtis]

I came across this post . Any thoughts specifically about the idea of dedicating a CPU core for MPD?

According to the author: By running the MPD process on a dedicated CPU core, it removes the last bit of harshness from the playback and makes the sound even more “analog”.

Thats just the human mind convincing itself of such things. 

The fact is that MPD (and most other softwares) are specifically designed as multi-threaded applications that take advantage of multi-core CPU's. You never want to deliberately cram this type of application into a single CPU core :-0

Have a look below at the MPD + CamillaDSP process maps on a 4-core CPU and notice that separate threads of execution are created for specific parts of their main processes. The Linux kernel scheduler manages which physical CPU core a given thread is executed on. What this accomplishes is a high degree of execution parallelism allowing the application to attain max responsiveness, performance and efficiency.

- PID is the process id
- TID is the thread id
- CLS is the kernel scheduling class. TS (time sharing) is the default non-realtime class. FF is realtime FIFO.
- RTPRIO is the realtime priority (1 - 99) where 1 is highest priority.
- PSR is the processor core the thread last ran on

MPD

Code:

pi@moode9:~ $ ps H -q `pidof -s mpd` -o 'pid,tid,cls,rtprio,comm,pcpu psr'
   PID     TID CLS RTPRIO COMMAND         %CPU PSR
 43503   43503  TS      - mpd              0.9   1
 43503   43504  TS      - io               0.0   3
 43503   43505  FF     40 rtio             0.0   0
 43503   43719  TS      - player           0.0   1
 43503   43720  TS      - decoder:faad     0.8   2
 43503   43723  FF     40 output:ALSA Def  0.0   1
 43503   43782  TS      - pcm-io           0.0   0

 CamillaDSP

Code:

pi@moode9:~ $ ps H -q `pidof -s camilladsp` -o 'pid,tid,cls,rtprio,comm,pcpu psr'
  PID     TID CLS RTPRIO COMMAND         %CPU PSR
43724   43724  TS      - camilladsp       0.6   2
43724   43725  TS      - flexi_logger-as  0.0   2
43724   43726  TS      - flexi_logger-fl  0.0   1
43724   43727  TS      - camilladsp       0.0   0
43724   43728  TS      - camilladsp       0.0   2
43724   43729  TS      - camilladsp       0.0   2
43724   43731  TS      - camilladsp       0.1   1
43724   43732  TS      - AlsaPlayback     0.2   0
43724   43733  TS      - FileCapture      0.2   3

You can also run these commands inside a watch command and see the kernel scheduler in action as it seamlessly reassigns processor cores (in microseconds) as needed. The -n option is the interval in secs that tells watch how often to run the command.

Code:

watch -n .1 "ps H -q `pidof -s mpd` -o 'pid,tid,cls,rtprio,comm,pcpu psr'"

Also keep in mind that there are a lot of other processes and threads in execution for example the web stack (PHP-FPM and NGINX), moode worker, monitors and watchdog daemons, networking, file management, renderers, etc etc.