Despite RT_GROUP_SCHED is only available on cgroup v1, there are still some users of this feature. General purpose distros (e.g. [1][2][3][4]) cannot enable CONFIG_RT_GROUP_SCHED easily: - since it prevents creation of RT tasks unless RT runtime is determined and distributed into cgroup tree, - grouping of RT threads is not what is desired by default on such systems, - it prevents use of cgroup v2 with RT tasks. This changeset aims at deferring the decision whether to have CONFIG_RT_GROUP_SCHED or not up until the boot time. By default RT groups are available as originally but the user can pass rt_group_sched=0 kernel cmdline parameter that disables the grouping and behavior is like with !CONFIG_RT_GROUP_SCHED (with certain runtime overhead). The series is organized as follows: 1) generic ifdefs cleanup, no functional changes, 2) preparing root_task_group to be used in places that take shortcuts in the case of !CONFIG_RT_GROUP_SCHED, 3) boot cmdline option that controls cgroup (v1) attributes, 4) conditional bypass of non-root task groups, 5) checks and comments refresh. The crux are patches: sched: Skip non-root task_groups with disabled RT_GROUP sched: Bypass bandwitdh checks with runtime disabled RT_GROUP_SCHED Futher notes: - it is not sched_feat() flag because that can be flipped any time - runtime disablement is not implemented as infinite per-cgroup RT limit since that'd still employ group scheduling which is unlike !CONFIG_RT_GROUP_SCHED RFC notes: - there remain two variants of various functions for CONFIG_RT_GROUP_SCHED and !CONFIG_RT_GROUP_SCHED, those could be folded into one and runtime evaluated guards in the folded functions could be used (I haven't posted it yet due to unclear performance benefit) - I noticed some lockdep issues over rt_runtime_lock but those are also in an unpatched kernel (and they seem to have been present since a long time without complications) [1] Debian (https://salsa.debian.org/kernel-team/linux/-/blob/debian/latest/debian/config/kernelarch-x86/config), [2] ArchLinux (https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/blob/main/config), [3] Fedora (https://src.fedoraproject.org/rpms/kernel/blob/rawhide/f/kernel-x86_64-fedora.config) [4] openSUSE TW (https://github.com/SUSE/kernel-source/blob/stable/config/x86_64/default) Michal Koutný (9): sched: Convert CONFIG_RT_GROUP_SCHED macros to code conditions sched: Remove unneeed macro wrap sched: Always initialize rt_rq's task_group sched: Add commadline option for RT_GROUP_SCHED toggling sched: Skip non-root task_groups with disabled RT_GROUP_SCHED sched: Bypass bandwitdh checks with runtime disabled RT_GROUP_SCHED sched: Do not construct nor expose RT_GROUP_SCHED structures if disabled sched: Add RT_GROUP WARN checks for non-root task_groups sched: Add annotations to RT_GROUP_SCHED fields .../admin-guide/kernel-parameters.txt | 5 ++ init/Kconfig | 11 +++ kernel/sched/core.c | 69 +++++++++++++++---- kernel/sched/rt.c | 51 +++++++++----- kernel/sched/sched.h | 34 +++++++-- kernel/sched/syscalls.c | 5 +- 6 files changed, 137 insertions(+), 38 deletions(-) base-commit: f92f4749861b06fed908d336b4dee1326003291b -- 2.47.1
