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

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Message-ID: <7hv81f78cy.fsf@baylibre.com>
Date: Mon, 08 Jul 2024 16:49:01 -0700
From: Kevin Hilman <khilman@...nel.org>
To: Celeste Liu <coelacanthushex@...il.com>, Heinrich Schuchardt
 <heinrich.schuchardt@...onical.com>, Anup Patel <anup@...infault.org>, Guo
 Ren <guoren@...nel.org>, Palmer Dabbelt <palmer@...osinc.com>, Paul
 Walmsley <paul.walmsley@...ive.com>, Huacai Chen <chenhuacai@...nel.org>,
 WANG Xuerui <kernel@...0n.name>, Thomas Bogendoerfer
 <tsbogend@...ha.franken.de>, Vladimir Kondratiev
 <vladimir.kondratiev@...ileye.com>, Gregory CLEMENT
 <gregory.clement@...tlin.com>, Théo Lebrun
 <theo.lebrun@...tlin.com>,
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin
 <npiggin@...il.com>, Christophe Leroy <christophe.leroy@...roup.eu>,
 "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>, Sven Joachim
 <svenjoac@....de>, Yoshinori Sato <ysato@...rs.sourceforge.jp>, Rich
 Felker <dalias@...c.org>, John Paul Adrian Glaubitz
 <glaubitz@...sik.fu-berlin.de>, Russell King <linux@...linux.org.uk>,
 Florian Fainelli <florian.fainelli@...adcom.com>, Ray Jui
 <rjui@...adcom.com>, Scott Branden <sbranden@...adcom.com>, Broadcom
 internal kernel review list <bcm-kernel-feedback-list@...adcom.com>, Tony
 Lindgren <tony@...mide.com>, Thierry Reding <thierry.reding@...il.com>,
 Jonathan Hunter <jonathanh@...dia.com>, Arnd Bergmann <arnd@...db.de>,
 Mykola Lysenko <mykolal@...com>, linux-riscv@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org,
 linux-rpi-kernel@...ts.infradead.org, linux-omap@...r.kernel.org,
 linux-tegra@...r.kernel.org, loongarch@...ts.linux.dev,
 linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
 linux-sh@...r.kernel.org
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>, Celeste Liu <CoelacanthusHex@...il.com>
Subject: Re: [PATCH 6/6] arm: defconfig: drop RT_GROUP_SCHED=y from
 bcm2855/tegra/omap2plus

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>