Re: [PATCH 6/6] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2855/tegra/omap2plus

[Celeste Liu <coelacanthushex@gmail.com>]

On 2024-07-09 20:26, Stefan Wahren wrote:
> Hi Celeste,
> 
> there is a typo in the subject line
> 
> s/bcm2855/bcm2835

Will be included in next version.

> 
> Am 09.07.24 um 01:49 schrieb Kevin Hilman:
>> Celeste Liu <coelacanthushex@gmail.com> writes:
>>
>>> Commit 673ce00c5d6c ("ARM: omap2plus_defconfig: Add support for distros
>>> with systemd") said it's because of recommendation from systemd. But
>>> systemd changed their recommendation later.[1]
>>>
>>> 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.
>>>
>>> [1]: https://github.com/systemd/systemd/commit/f4e74be1856b3ac058acbf1be321c31d5299f69f
>>> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
>>>
>>> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com>
>>> ---
>>>   arch/arm/configs/bcm2835_defconfig   | 1 -
>>>   arch/arm/configs/omap2plus_defconfig | 1 -
>>>   arch/arm/configs/tegra_defconfig     | 1 -
>> For omap2plus_defconfig:
>>
>> Acked-by: Kevin Hilman <khilman@baylibre.com>
>>
>>
> For bcm2835_defconfig:
> 
> Tested-by: Stefan Wahren <wahrenst@gmx.net>