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Subject: Re: [PATCH 2/6] loongarch: defconfig: drop RT_GROUP_SCHED=y
From: Xi Ruoyao <xry111@xry111.site>
To: Celeste Liu <coelacanthushex@gmail.com>, Heinrich Schuchardt
 <heinrich.schuchardt@canonical.com>, Anup Patel <anup@brainfault.org>, Guo
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Cc: linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, 
	linux-kernel@vger.kernel.org, Lennart Poettering <lennart@poettering.net>, 
 Icenowy Zheng
	 <uwu@icenowy.me>
Date: Thu, 30 May 2024 19:27:32 +0800
In-Reply-To: <20240530111947.549474-10-CoelacanthusHex@gmail.com>
References: <20240530111947.549474-8-CoelacanthusHex@gmail.com>
	 <20240530111947.549474-10-CoelacanthusHex@gmail.com>
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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" hierarch=
y it
> needs an RT budget assigned, otherwise the processes in it will not be ab=
le to
> get RT at all. The problem with RT group scheduling is that it requires t=
he
> budget assigned but there's no way we could assign a default budget, sinc=
e 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 c=
ome up
> with values that would work by default in the general case.[1]
>=20
> For cgroup v2, it's almost unusable as well. If it turned on, the cpu con=
troller
> 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.
>=20
> Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also doesn=
't
> support it.[2]
>=20
> [1]: https://bugzilla.redhat.com/show_bug.cgi?id=3D1229700
> [2]: https://github.com/systemd/systemd/issues/13781#issuecomment-5491643=
83
>=20
> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com>

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

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

> ---
> =C2=A0arch/loongarch/configs/loongson3_defconfig | 1 -
> =C2=A01 file changed, 1 deletion(-)
>=20
> 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=3Dy
> =C2=A0CONFIG_MEMCG=3Dy
> =C2=A0CONFIG_BLK_CGROUP=3Dy
> =C2=A0CONFIG_CFS_BANDWIDTH=3Dy
> -CONFIG_RT_GROUP_SCHED=3Dy
> =C2=A0CONFIG_CGROUP_PIDS=3Dy
> =C2=A0CONFIG_CGROUP_RDMA=3Dy
> =C2=A0CONFIG_CGROUP_FREEZER=3Dy

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University