Re: [PATCH v2 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y

[Conor Dooley <conor.dooley@microchip.com>]

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On Fri, Aug 23, 2024 at 01:43:26AM +0800, Celeste Liu wrote:
> 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
> 
> Fixes: ba6cfef057e1 ("riscv: enable Docker requirements in defconfig")

I don't think this fixes tag is suitable, the commit you cite in
moby/docker is a year younger than the one in the fixes tag, so it was
correct at the time it was written. I think the fixes tag should just be
removed, since that commit was not wrong. Or am I missing something?

> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com>
> ---
>  arch/riscv/configs/defconfig | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
> index 12dc8c73a8ac..de85c3ab261e 100644
> --- a/arch/riscv/configs/defconfig
> +++ b/arch/riscv/configs/defconfig
> @@ -9,7 +9,6 @@ CONFIG_CGROUPS=y
>  CONFIG_MEMCG=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
> 
> -- 
> 2.46.0
> 

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