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Thu, 16 Jan 2025 10:04:19 -0800 (PST) Received: from [10.67.48.245] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-21c2ceb9b3asm3086255ad.75.2025.01.16.10.04.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 16 Jan 2025 10:04:18 -0800 (PST) Message-ID: <967278a1-a2e9-44c3-90ee-ae9a57a54421@broadcom.com> Date: Thu, 16 Jan 2025 10:04:14 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 4/4] arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus To: Celeste Liu , Paul Walmsley , Palmer Dabbelt , Albert Ou , Guo Ren , Anup Patel , Heinrich Schuchardt , Huacai Chen , WANG Xuerui , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , Russell King , Broadcom internal kernel review list , Ray Jui , Scott Branden , Tony Lindgren , Thierry Reding , Jonathan Hunter , Aaro Koskinen , Andreas Kemnade , Kevin Hilman , Roger Quadros Cc: Palmer Dabbelt , 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, Stefan Wahren , Thierry Reding References: <20250115-fix-riscv-rt_group_sched-v4-0-607606fe73a5@coelacanthus.name> <20250115-fix-riscv-rt_group_sched-v4-4-607606fe73a5@coelacanthus.name> Content-Language: en-US From: Florian Fainelli Autocrypt: addr=florian.fainelli@broadcom.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/14/25 12:41, Celeste Liu wrote: > 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 > > Tested-by: Stefan Wahren > Acked-by: Kevin Hilman > Acked-by: Thierry Reding > Signed-off-by: Celeste Liu > --- > arch/arm/configs/bcm2835_defconfig | 1 - Acked-by: Florian Fainelli # bcm2835_defconfig -- Florian