[REQUEST] Aggregate child process values in tree mode

[magneticflux-]

Is your feature request related to a problem? Please describe.
I'd like to view the process tree, but also sort by total child CPU usage so that (non-collapsed) subtrees with a lot of resource usage appear higher.

Describe the solution you'd like
An option to report aggregate statistics about child processes regardless of the nodes being collapsed or not.

Describe alternatives you've considered
Introduce another toggle like per-core called aggregate?

Additional context
This seems mostly-implemented already since collapsed nodes already sum their values, I'd just like to see the sums while also seeing the child processes.

[imwints]

I've implemented this in https://github.com/nobounce/btop/tree/aggregate-child-processes, but I find this hardly distinguishable from the normal per-process statistics. Any idea how this could be made visible that this is the combined resource usage so user won't freak out if they are not aware of this and see for example /sbin/init using 5 gigs of memory?

Also maybe have a look add my wording of this setting, might not describe this feature as you've intended it.

[magneticflux-]

Awesome that works perfectly! It makes a huge difference when there's deeply-nested trees and I want to show the most "active" ones first, like compiling a bunch of packages in NixOS.

Details

Overriding the btop package in Nix to use this branch:

(btop.overrideAttrs (prev: {
  name = "btop/aggregate-child-processes";
  src = pkgs.fetchFromGitHub {
    owner = "nobounce";
    repo = "btop";
    rev = "aggregate-child-processes";
    hash = "sha256-wWpcqnZXBH4nIE/EzWWooFyzM0odX2ewAHq1fIuX5M8=";
  };
}))

Before this, the systemd/sshd/nixos-rebuild tree wasn't guaranteed to be at the top because random background services with 2% CPU usage got sorted above sshd with 1%, even though the tree was a lot more active.

---

To make it explicitly clear to users, you could split the display of values into "self" and "child" parts, so something like /sbin/init spawning a child with 5G memory would look like 1.6M + 5G. The downside is that it's much wider than the original.

In my opinion, having the aggregate stats option default to off and making the description really clear is a good approach if you're concerned about confusion. I suggest the description be:

In tree-view, include all child resources with the parent even while expanded.

[imwints]

I just realized that if we show both memory values we would also want to show all of the other resources twice, but that would take up to much space (or I just can't imagine a nicer way of doing things)