linux-kernel - Re: [PATCH 6/6] arm: defconfig: drop RT_GROUP

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Message-ID: <44535d2d-c95d-4673-b845-032669cf7abf@gmail.com>
Date: Tue, 9 Jul 2024 20:45:38 +0800
From: Celeste Liu <coelacanthushex@...il.com>
To: Stefan Wahren <wahrenst@....net>, Kevin Hilman <khilman@...nel.org>,
 Vladimir Kondratiev <vladimir.kondratiev@...ileye.com>,
 Florian Fainelli <florian.fainelli@...adcom.com>, Ray Jui
 <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>
Cc: linux-kselftest@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org, Lennart Poettering <lennart@...ttering.net>,
 Icenowy Zheng <uwu@...nowy.me>, Théo Lebrun
 <theo.lebrun@...tlin.com>, Gregory CLEMENT <gregory.clement@...tlin.com>,
 Michael Ellerman <mpe@...erman.id.au>,
 "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>, Sven Joachim
 <svenjoac@....de>, Huacai Chen <chenhuacai@...nel.org>,
 Heinrich Schuchardt <heinrich.schuchardt@...onical.com>,
 Anup Patel <anup@...infault.org>, Nicholas Piggin <npiggin@...il.com>,
 Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
 Jonathan Hunter <jonathanh@...dia.com>,
 Christophe Leroy <christophe.leroy@...roup.eu>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Rich Felker <dalias@...c.org>,
 Russell King <linux@...linux.org.uk>, Tony Lindgren <tony@...mide.com>,
 Guo Ren <guoren@...nel.org>, linux-tegra@...r.kernel.org,
 Thierry Reding <thierry.reding@...il.com>, linux-riscv@...ts.infradead.org,
 Arnd Bergmann <arnd@...db.de>, linux-arm-kernel@...ts.infradead.org,
 linux-omap@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
 linux-sh@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-mips@...r.kernel.org, loongarch@...ts.linux.dev,
 Mykola Lysenko <mykolal@...com>, Yoshinori Sato
 <ysato@...rs.sourceforge.jp>, Paul Walmsley <paul.walmsley@...ive.com>,
 John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
 linux-rpi-kernel@...ts.infradead.org, WANG Xuerui <kernel@...0n.name>
Subject: Re: [PATCH 6/6] arm: defconfig: drop RT_GROUP_SCHED=y from
 bcm2855/tegra/omap2plus

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@...il.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@...il.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@...libre.com>
>>
>>
> For bcm2835_defconfig:
> 
> Tested-by: Stefan Wahren <wahrenst@....net>