Re: [PATCH v3 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y

From: Charlie Jenkins <charlie@rivosinc.com>
To: Celeste Liu <coelacanthushex@gmail.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>, Guo Ren <guoren@kernel.org>,
	Anup Patel <anup@brainfault.org>,
	Heinrich Schuchardt <heinrich.schuchardt@canonical.com>,
	Huacai Chen <chenhuacai@kernel.org>,
	WANG Xuerui <kernel@xen0n.name>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Russell King <linux@armlinux.org.uk>,
	Florian Fainelli <florian.fainelli@broadcom.com>,
	Broadcom internal kernel review list
	<bcm-kernel-feedback-list@broadcom.com>,
	Ray Jui <rjui@broadcom.com>,
	Scott Branden <sbranden@broadcom.com>,
	Tony Lindgren <tony@atomide.com>,
	Thierry Reding <thierry.reding@gmail.com>,
	Jonathan Hunter <jonathanh@nvidia.com>,
	Palmer Dabbelt <palmer@rivosinc.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	loongarch@lists.linux.dev, linux-sh@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-rpi-kernel@lists.infradead.org, linux-omap@vger.kernel.org,
	linux-tegra@vger.kernel.org
Subject: Re: [PATCH v3 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y
Date: Thu, 12 Sep 2024 13:58:05 -0700	[thread overview]
Message-ID: <ZuNV3ewTH63lb972@ghost> (raw)
In-Reply-To: <20240910-fix-riscv-rt_group_sched-v3-1-486e75e5ae6d@gmail.com>

On Tue, Sep 10, 2024 at 08:51:07PM +0800, Celeste Liu wrote:
> Commit ba6cfef057e1 ("riscv: enable Docker requirements in defconfig")
> introduced it because of Docker, but Docker has removed this requirement
> since [1] (2023-04-19).
> 
> 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.[3]
> 
> [1]: https://github.com/moby/moby/commit/005150ed69c540fb0b5323e0f2208608c1204536
> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=1229700
> [3]: https://github.com/systemd/systemd/issues/13781#issuecomment-549164383
> 
> Acked-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> Signed-off-by: Celeste Liu <CoelacanthusHex@gmail.com>

Acked-by: Charlie Jenkins <charlie@rivosinc.com>

> ---
>  arch/riscv/configs/defconfig | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/arch/riscv/configs/defconfig b/arch/riscv/configs/defconfig
> index 12dc8c73a8acfaa5c8f442968a807de303428d9e..de85c3ab261e6d62b2089a3c89bdc9d1b34fa792 100644
> --- a/arch/riscv/configs/defconfig
> +++ b/arch/riscv/configs/defconfig
> @@ -9,7 +9,6 @@ CONFIG_CGROUPS=y
>  CONFIG_MEMCG=y
>  CONFIG_CGROUP_SCHED=y
>  CONFIG_CFS_BANDWIDTH=y
> -CONFIG_RT_GROUP_SCHED=y
>  CONFIG_CGROUP_PIDS=y
>  CONFIG_CGROUP_FREEZER=y
>  CONFIG_CGROUP_HUGETLB=y
> 
> -- 
> 2.46.0
> 
> 
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