building the rawhide kernel with cgroup-v2 cpu controller patches

[Zbigniew Jędrzejewski-Szmek]

Unfortunately, due to the disagreements in the kernel development
community, CPU controller cgroup v2 support has not been merged and
enabling it requires applying two small out-of-tree kernel
patches. The situation is explained in the following documentation:

https://git.kernel.org/cgit/linux/kernel/git/tj/cgroup.git/tree/Documenta...

While it isn't clear what will happen with CPU controller cgroup v2
support, there are critical features which are possible only on cgroup
v2 such as buffered write control making cgroup v2 essential for a lot
of workloads. Also we finally have reliable empty cgroup reporting which
avoids various systemd issues with zombie scope units and such.

Systemd recently gained experimental support for the new cgroup v2 cpu
controller [1], which of course only works for people who
a) are running with systemd.unified_cgroup_hierarchy=1 and
b) have a patched kernel. We would like to move closer towards
switching to v2 hierarchy, with an eye towards using unified hierarchy
by default, but we have a chicken and egg problem where we cannot
encourage people to switch and test systemd with v2 hierarchy,
since the kernel support is incomplete. And the kernel support does
not get enough testing because it's incomplete and requires a
substantive effort.

Would it be possible to compile the rawhide kernels with the cgroup-v2-cpu
patches [2]? This should cause no issue for v1 users, and would let the
kernel and systemd functionality get wider testing, and hopefully nudge the
kernel upstream towards finalizing the unified hierarchy support.

Zbyszek

[1] https://github.com/systemd/systemd/commit/5f9a610ad2b3200a3
[2] https://git.kernel.org/cgit/linux/kernel/git/tj/cgroup.git/log/?h=cgroup-...