linux-kernel - Re: [PATCH 3/6] mips: defconfig: drop RT_GROUP

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Date: Tue, 11 Jun 2024 10:41:16 +0200
From: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To: Celeste Liu <coelacanthushex@...il.com>
Cc: 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>,
	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, linux-kselftest@...r.kernel.org,
	bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lennart Poettering <lennart@...ttering.net>,
	Icenowy Zheng <uwu@...nowy.me>
Subject: Re: [PATCH 3/6] mips: defconfig: drop RT_GROUP_SCHED=y from
 generic/db1xxx/eyeq5

On Thu, May 30, 2024 at 07:19:51PM +0800, Celeste Liu wrote:
> 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.[1]
> 
> 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.[2]
> 
> [1]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
> [2]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383
> 
> Signed-off-by: Celeste Liu <CoelacanthusHex@...il.com>
> ---
>  arch/mips/configs/db1xxx_defconfig  | 1 -
>  arch/mips/configs/eyeq5_defconfig   | 1 -
>  arch/mips/configs/generic_defconfig | 1 -
>  3 files changed, 3 deletions(-)

applied to mips-next.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]