[PATCHSET v2 sched_ext/for-6.12] sched_ext: Add cgroup support

[Tejun Heo <tj@kernel.org>]

This is v2 of sched_ext cgroup support patchset. Changes from v1
(http://lkml.kernel.org/r/20240808002550.731248-1-tj@kernel.org) are:

- cgroup interface file visiblity toggling based on SCX_OPS flags is dropped
  as it caused more confusion than helping anything. sched_ext now just
  warns when unimplemented features are used.

This was originally taken from the cgroup integration part of the sched_ext
v6 patchset:

  http://lkml.kernel.org/r/20240501151312.635565-1-tj@kernel.org

This patchset is on top of sched_ext/for-6.12 (9ad2861b773d ("sched_ext:
Allow dequeue_task_scx to fail")) and contains the following patches:

 0001-sched-Expose-css_tg.patch
 0002-sched-Make-cpu_shares_read_u64-use-tg_weight.patch
 0003-sched-Introduce-CONFIG_GROUP_SCHED_WEIGHT.patch
 0004-sched_ext-Add-cgroup-support.patch
 0005-sched_ext-Add-a-cgroup-scheduler-which-uses-flattene.patch

 0001-0003 are sched core preparations. Straightforward. No functional
 changes.

 0004 adds cgroup support to sched_ext.

 0005 implements an example scheduler which uses the cgroup support.

The patchset is also available in the following git branch:

 git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext.git scx-cgroup-v2

diffstat follows. Thanks.

 include/linux/sched/ext.h                       |    3
 init/Kconfig                                    |   10
 kernel/sched/core.c                             |   98 +++-
 kernel/sched/ext.c                              |  519 ++++++++++++++++++++++++-
 kernel/sched/ext.h                              |   22 +
 kernel/sched/sched.h                            |   14
 tools/sched_ext/Makefile                        |    2
 tools/sched_ext/README.md                       |   12
 tools/sched_ext/include/scx/common.bpf.h        |    1
 tools/sched_ext/scx_flatcg.bpf.c                |  949 ++++++++++++++++++++++++++++++++++++++++++++++
 tools/sched_ext/scx_flatcg.c                    |  233 +++++++++++
 tools/sched_ext/scx_flatcg.h                    |   51 ++
 tools/testing/selftests/sched_ext/maximal.bpf.c |   32 +
 13 files changed, 1906 insertions(+), 40 deletions(-)

--
tejun