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

[Heinrich Schuchardt]

On 09.09.24 14:14, Celeste Liu wrote:
> On 2024-09-09 19:53, Conor Dooley wrote:
> 
>> 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?
> 
> The Docker commit I cited introduce the fix, not the bug. So it should be later
> than commit in fixes tag, otherwise Heinrich Schuchardt won't pick the wrong
> config from upstream.
> 
> Timeline is:
> 1) 2015-06-19 Qiang Huang introduce RT_GROUP_SCHED check in Docker.[1]
> 2) 2022-06-08 Heinrich Schuchardt pick this to defconfig in commit
>                in fixes tag.
> 3) 2023-04-19 Florian Schmaus remove this requirement from Docker in
>                commit I cited.
> 
> [1]: https://github.com/moby/moby/commit/fb85a99f5899df7475ba6b1ac4b2e1d32974eca2

I experience no problems running Docker without CONFIG_RT_GROUP_SCHED on 
Ubuntu 24.04.

The Docker patch is only for contrib/check-config.sh. Probably Docker at 
the time of my patch would have worked without CONFIG_RT_GROUP_SCHED, 
too. I have no issue with the Fixes: tag in this patch.

Acked-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>

> 
>>
>>> Signed-off-by: Celeste Liu <CoelacanthusHex at 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
>>>
>