Extending cpuset to include user processes

[Snoopy8]

Some more information for next release of cpuset:

1. cpuset does not stop IRQs from using the user cpuset (CPUs 2,3).  Ideally, to reduce latency, IRQs should be on a different CPU to the music player.  My workaround is to edit
   /etc/default/irqbalance and set IRQBALANCE_BANNED_CPUS=C  (hex mask value, run in CPUs 0,1 not in CPUs 2,3)
   
2. This may help with setting a new cpuset for a user process.  CamillaDSP was started as a system process at boot. Manually shifted using
   sudo cset proc --move --toset=user --pid 723 --threads
   
   Confirmed move worked using cset shield --shield -v  
   Code:

   cset: "user" cpuset of CPUSPEC(2-3) with 11 tasks running
   USER       PID  PPID SPPr TASK NAME
   -------- ----- ----- ---- ---------
   root       723     1 Sf70 [camilladsp]
   root       738     1 Sf70 [camilladsp]
   root       746     1 Sf70 [camilladsp]
   root       747     1 Sf70 [AlsaPlayback]
   root       748     1 Sf70 [AlsaCapture]
   root      2125     1 Soth [mpd]
   root      2174     1 Soth [io]
   root      2175     1 Sf40 [rtio]
   root      2178     1 Soth [player]
   root      2182     1 Soth [decoder]
   root      2387     1 Sf40 [output]
cset: done
3. Some issues with existing cpuset, a few player processes were not shifted to the user cpuset
   LMS + Squeezlite R2 : squeeze2upnp-x8  (using DLNA/UPnP bridge) remained in the system cpuset
   LMS + upmpdcli : squeeze2upnp-x8, mpd  remained in the system cpuset
   Minimserver : uses Java which remained in the system cpuset
   

Can confirm SQ improved with shifting IRQs to system cpuset and CamillaDSP to user cpuset.

*****
Added 22-Jun

A few more notes

1.  Can move a few more kernel processes from user to system cpuset using
   sudo cset shield -k on
   While I heard no discernible difference with SQ, for completeness, should include this.
   
2. With upmpdcli,  it is not possible to shift the underlying mpd process from system to user cpuset.  Given that upmpdcli is only a wrapper and the work is done by mpd, cpuset may not provide a SQ benefit for upmpdcli?
   
3. Tried dedicating a cpu to LMS and another cpu to Squeezelite R2.  No difference in SQ to running both LMS and Squeezelite R2 in same cpu.
   
4. Similarly no difference in SQ with mpd and CamillaDSP running on same cpu or on separate individual cpus.
   
5. However, with cpu intensive servers like Roon or HQplayer, there may be a benefit in running their players on a seperate cpu?  Someone should test this.
   
6. If mympd is enabled (coming in next release), should shift it from system to user cpuset. I do not use mympd and will disable it.