Add option to show processes within a cgroup in cgroup view

[Flowdalic]

In #8114 it was stated that "Personally, I think cgroup view is much more informative. Process names are often named really strangely and is not very informative.". This can be true, but not in every case.

Consider for example this cgroup view that below presents:

│└─ user.slice                                      190.94%    20.6 GB    0.07%          0.00%          14.10%         21.1 MB/s  111.7 MB/s 132.8 MB/s 53               15                     1805                                                                                     |│
│   └─ user-1000.slice                              190.94%    20.5 GB    0.08%          0.00%          13.62%         21.1 MB/s  111.7 MB/s 132.8 MB/s 52               12                     1805                                                                                     |│
│      └─ session-3.scope                           1.43%      1 GB       0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      34                                                                                       |│
│      └─ user@1000.service                         189.51%    19.5 GB    0.10%          0.00%          13.60%         21.1 MB/s  111.7 MB/s 132.8 MB/s 50               12                     1771                                                                                     |│
│         └─ app.slice                              189.54%    19.5 GB    0.10%          0.00%          13.71%         21.1 MB/s  111.7 MB/s 132.8 MB/s 36               12                     1684                                                                                     |│
│            └─ app-git\x2dmaintenance.slice        0.00%      1.8 GB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                4                      0                                                                                        |│
│            └─ app-gnome-Nextcloud-64991.scope     0.01%      102.3 MB   0.00%          0.13%          0.13%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      16                                                                                       |│
│            └─ app-gnome-blueman-65005.scope       0.04%      19.8 MB    0.00%          0.00%          0.00%          ?          ?          ?          0                0                      10                                                                                       |│
│            └─ app-gnome-herbstluftwm-64986.scope  1.39%      888.8 MB   0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      81                                                                                       |│
│            └─ app-gnome-org.gnome.Evolution\x2dal 0.00%      3.6 MB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      8                                                                                        |│
│            └─ app-gnome\x2dsession\x2dmanager.sli 0.00%      3.4 MB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    1                0                      5                                                                                        |│
│               └─ gnome-session-manager@gnome-flas 0.00%      3.4 MB     0.00%          0.00%          0.00%          ?          ?          ?          0                0                      5                                                                                        |│
│            └─ app-rofi-google\x2dchrome\x2dstable 8.81%      4.6 GB     0.13%          0.00%          7.14%          0.0 B/s    2.3 MB/s   2.3 MB/s   0                0                      1100                                                                                     |│
│            └─ app-rofi-thunderbird-162.service    69.83%     1.4 GB     0.12%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      114                                                                                      |│
│            └─ atuin-daemon.service                0.02%      58.7 MB    0.00%          0.00%          0.88%          0.0 B/s    16.6 KB/s  16.6 KB/s  0                0                      4                                                                                        |│
│            └─ dbus.socket                         0.00%      0.0 B      0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      0                                                                                        ▒│
│            └─ dconf.service                       0.00%      444 KB     0.00%          0.00%          0.00%          ?          ?          ?          0                0                      4                                                                                        ▒│
│            └─ dirmngr.service                     0.00%      3.3 MB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      1                                                                                        ▒│
│            └─ dunst.service                       0.00%      4.5 MB     0.00%          0.00%          0.00%          ?          ?          ?          0                0                      6                                                                                        ▒│
│            └─ emacs-29.service                    0.00%      91.2 MB    0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      5                                                                                        ▒│
│            └─ evolution-addressbook-factory.servi 0.00%      2 MB       0.00%          0.00%          0.00%          ?          ?          ?          0                0                      7                                                                                        ▒│
│            └─ evolution-calendar-factory.service  0.00%      1.9 MB     0.00%          0.00%          0.00%          ?          ?          ?          0                0                      10                                                                                       ▒│
│            └─ evolution-source-registry.service   0.00%      2 MB       0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      5                                                                                        ▒│
│            └─ gnome-keyring-daemon.service        0.00%      2.3 MB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      6                                                                                        ▒│
│            └─ gnome-session-monitor.service       0.00%      612 KB     0.00%          0.00%          0.00%          ?          ?          ?          0                0                      2                                                                                        ▒│
│            └─ kitty-102799-0.scope                0.00%      246 MB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      10                                                                                       ▒│
│            └─ kitty-106668-0.scope                55.63%     4.1 GB     0.22%          0.00%          9.33%          16.4 MB/s  1.6 KB/s   16.4 MB/s  0                0                      13                                                                                       ▒│
│            └─ kitty-139855-0.scope                0.00%      36.6 MB    0.00%          0.00%          0.00%          0.0 B/s    201.9 KB/s 201.9 KB/s 0                0                      24                                                                                       ▒│
│            └─ kitty-141847-0.scope                0.00%      18.5 MB    0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      1                                                                                        ▒│
│            └─ kitty-145762-0.scope                0.00%      1.1 GB     0.00%          0.00%          0.00%          0.0 B/s    0.0 B/s    0.0 B/s    0                0                      10                                                                                       ▒│
│            └─ kitty-146047-0.scope                0.49%      2.3 GB     0.00%          0.00%          32.19%         4.6 MB/s   13.3 MB/s  18 MB/s    0                0                      2                                                                                        ▒│
│            └─ kitty-146185-0.scope                36.41%     1.9 GB     0.43%          0.00%          1.66%          0.0 B/s    95.9 MB/s  95.9 MB/s  0                0                      2             

Here, the terminal kitty does the right thing™ and creates a scope for every terminal window. However, just looking at the cgroup view, does not tell me what exactly it is that kitty-106668-0.scope is performing creating some CPU load.

If the processes with their arguments where listed as descendants of kitty-106668-0.scope, I would in many cases immediately get an idea what is running there and what it is doing. Right now, I have to zoom (via z) into the cgroup to see its processes.

BTW, thanks for below, it is IMHO currently the best tool for cgroup-based performance-metric analysis.