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Tue, 14 Jan 2025 15:41:54 -0500 (EST) From: Celeste Liu Subject: [PATCH v4 0/4] defconfig: drop RT_GROUP_SCHED=y Date: Wed, 15 Jan 2025 04:41:19 +0800 Message-Id: <20250115-fix-riscv-rt_group_sched-v4-0-607606fe73a5@coelacanthus.name> MIME-Version: 1.0 X-B4-Tracking: v=1; b=H4sIAO/LhmcC/33OTWrDMBAF4KsErTtBksc/6arQTe8QSlCksSWIr TByRELw3Suni2TTbgYezPt4d5GIAyXxvrkLphxSiFMJ+LYR1ptpIAiuZKGlRtnoFvpwBQ7JZuD 5MHC8nA/JenLgNEmFR8LOGVHqZ6by+6D33yX3HEeYPZN5gnUllVI7bLc1lovQwWekk7Fmmv0lf dH1YxhNOG1tHFfThzRHvj3WZr3Kv06nq7+HZQ0SCN3RkMa+JfVirsNy9YR2Sv4DVQXCrqG2ptp Q416hZVl+ALc/HAZNAQAA X-Change-ID: 20240627-fix-riscv-rt_group_sched-d2e014be48da To: 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 , Florian Fainelli , 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, Charlie Jenkins , Celeste Liu , Xi Ruoyao , Stefan Wahren , Thierry Reding X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; 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X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 --- Changes in v4: - Update Acked-by - Link to v3: https://lore.kernel.org/r/20240910-fix-riscv-rt_group_sched-v3-0-486e75e5ae6d@gmail.com Changes in v3: - Remove Fixes: tag because of it's not suitable. - Link to v2: https://lore.kernel.org/r/20240823-fix-riscv-rt_group_sched-v2-0-e4dbae24f7e1@gmail.com Changes in v2: * Remove MIPS and PowerPC patch because of merged. * Link to v1: https://lore.kernel.org/lkml/20240530111947.549474-8-CoelacanthusHex@gmail.com/T Celeste Liu (6): riscv: defconfig: drop RT_GROUP_SCHED=y loongarch: defconfig: drop RT_GROUP_SCHED=y sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell arm: defconfig: drop RT_GROUP_SCHED=y from bcm2855/tegra/omap2plus arch/arm/configs/bcm2835_defconfig | 1 - arch/arm/configs/omap2plus_defconfig | 1 - arch/arm/configs/tegra_defconfig | 1 - arch/loongarch/configs/loongson3_defconfig | 1 - arch/riscv/configs/defconfig | 1 - arch/sh/configs/sdk7786_defconfig | 1 - arch/sh/configs/urquell_defconfig | 1 - 7 files changed, 7 deletions(-) -- 2.45.1 --- Celeste Liu (4): riscv: defconfig: drop RT_GROUP_SCHED=y loongarch: defconfig: drop RT_GROUP_SCHED=y sh: defconfig: drop RT_GROUP_SCHED=y from sdk7786/urquell arm: defconfig: drop RT_GROUP_SCHED=y from bcm2835/tegra/omap2plus arch/arm/configs/bcm2835_defconfig | 1 - arch/arm/configs/omap2plus_defconfig | 1 - arch/arm/configs/tegra_defconfig | 1 - arch/loongarch/configs/loongson3_defconfig | 1 - arch/riscv/configs/defconfig | 1 - arch/sh/configs/sdk7786_defconfig | 1 - arch/sh/configs/urquell_defconfig | 1 - 7 files changed, 7 deletions(-) --- base-commit: 0e287d31b62bb53ad81d5e59778384a40f8b6f56 change-id: 20240627-fix-riscv-rt_group_sched-d2e014be48da Best regards,