linux-kernel - Re: [PATCH 2/6] loongarch: defconfig: drop RT_GROUP

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Date: Thu, 30 May 2024 19:27:32 +0800
From: Xi Ruoyao <xry111@...111.site>
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>
Subject: Re: [PATCH 2/6] loongarch: defconfig: drop RT_GROUP_SCHED=y

On Thu, 2024-05-30 at 19:19 +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>

As a distro maintainer who had once been bitten by this option:

Reviewed-by: Xi Ruoyao <xry111@...111.site>

> ---
>  arch/loongarch/configs/loongson3_defconfig | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/loongarch/configs/loongson3_defconfig b/arch/loongarch/configs/loongson3_defconfig
> index b4252c357c8e..4d93adb3f1a2 100644
> --- a/arch/loongarch/configs/loongson3_defconfig
> +++ b/arch/loongarch/configs/loongson3_defconfig
> @@ -23,7 +23,6 @@ CONFIG_NUMA_BALANCING=y
>  CONFIG_MEMCG=y
>  CONFIG_BLK_CGROUP=y
>  CONFIG_CFS_BANDWIDTH=y
> -CONFIG_RT_GROUP_SCHED=y
>  CONFIG_CGROUP_PIDS=y
>  CONFIG_CGROUP_RDMA=y
>  CONFIG_CGROUP_FREEZER=y

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University