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[97.126.77.189]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ca344c399csm596679a91.5.2024.07.08.16.49.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 08 Jul 2024 16:49:02 -0700 (PDT) From: Kevin Hilman To: Celeste Liu , Heinrich Schuchardt , Anup Patel , Guo Ren , Palmer Dabbelt , Paul Walmsley , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Vladimir Kondratiev , Gregory CLEMENT , =?utf-8?Q?Th=C3=A9o?= Lebrun , Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Naveen N . Rao" , Sven Joachim , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Russell King , Florian Fainelli , Ray Jui , Scott Branden , Broadcom internal kernel review list , Tony Lindgren , Thierry Reding , Jonathan Hunter , Arnd Bergmann , Mykola Lysenko , linux-riscv@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, linux-omap@vger.kernel.org, linux-tegra@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org Cc: linux-kselftest@vger.kernel.org, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, Lennart Poettering , Icenowy Zheng , Celeste Liu Subject: Re: [PATCH 6/6] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2855/tegra/omap2plus In-Reply-To: <20240530111947.549474-14-CoelacanthusHex@gmail.com> References: <20240530111947.549474-8-CoelacanthusHex@gmail.com> <20240530111947.549474-14-CoelacanthusHex@gmail.com> Date: Mon, 08 Jul 2024 16:49:01 -0700 Message-ID: <7hv81f78cy.fsf@baylibre.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Celeste Liu 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 > --- > 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