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[v4,1/4] riscv: defconfig: drop RT_GROUP_SCHED=y

Message ID 20250115-fix-riscv-rt_group_sched-v4-1-607606fe73a5@coelacanthus.name (mailing list archive)
State New
Headers show
Series defconfig: drop RT_GROUP_SCHED=y | expand

Commit Message

Celeste Liu Jan. 14, 2025, 8:41 p.m. UTC 
Commit ba6cfef057e1 ("riscv: enable Docker requirements in defconfig")
introduced it because of Docker, but Docker has removed this requirement
since [1] (2023-04-19).

For cgroup v1, if turned on, and there's any cgroup in the "cpu" hierarchy it
needs an RT budget assigned, otherwise the processes in it will not be able to
get RT at all. The problem with RT group scheduling is that it requires the
budget assigned but there's no way we could assign a default budget, since the
values to assign are both upper and lower time limits, are absolute, and need to
be sum up to < 1 for each individal cgroup. That means we cannot really come up
with values that would work by default in the general case.[2]

For cgroup v2, it's almost unusable as well. If it turned on, the cpu controller
can only be enabled when all RT processes are in the root cgroup. But it will
lose the benefits of cgroup v2 if all RT process were placed in the same cgroup.

Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn't
support it.[3]

[1]: https://github.com/moby/moby/commit/005150ed69c540fb0b5323e0f2208608c1204536
[2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
[3]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383

Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Celeste Liu <uwu@coelacanthus.name>
---
 arch/riscv/configs/defconfig | 1 -
 1 file changed, 1 deletion(-)
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Patch

diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
index b4a37345703eb35757419aa5a2b057c82ed22fda..46b8fb30726858a945a24097773174961c2f4d10 100644
--- a/arch/riscv/configs/defconfig
+++ b/arch/riscv/configs/defconfig
@@ -10,7 +10,6 @@  CONFIG_MEMCG=y
 CONFIG_BLK_CGROUP=y
 CONFIG_CGROUP_SCHED=y
 CONFIG_CFS_BANDWIDTH=y
-CONFIG_RT_GROUP_SCHED=y
 CONFIG_CGROUP_PIDS=y
 CONFIG_CGROUP_FREEZER=y
 CONFIG_CGROUP_HUGETLB=y