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Tue, 10 Sep 2024 05:57:59 -0700 (PDT) From: Celeste Liu X-Google-Original-From: Celeste Liu To: conor.dooley@microchip.com Cc: anup@brainfault.org, aou@eecs.berkeley.edu, bcm-kernel-feedback-list@broadcom.com, chenhuacai@kernel.org, coelacanthushex@gmail.com, dalias@libc.org, florian.fainelli@broadcom.com, glaubitz@physik.fu-berlin.de, guoren@kernel.org, heinrich.schuchardt@canonical.com, jonathanh@nvidia.com, kernel@xen0n.name, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-omap@vger.kernel.org, linux-riscv@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, linux-sh@vger.kernel.org, linux-tegra@vger.kernel.org, linux@armlinux.org.uk, loongarch@lists.linux.dev, palmer@dabbelt.com, palmer@rivosinc.com, paul.walmsley@sifive.com, rjui@broadcom.com, sbranden@broadcom.com, thierry.reding@gmail.com, tony@atomide.com, ysato@users.sourceforge.jp, Celeste Liu Subject: Re: [PATCH v2 1/4] riscv: defconfig: drop RT_GROUP_SCHED=y Date: Tue, 10 Sep 2024 20:57:30 +0800 Message-ID: <20240910125729.480594-2-CoelacanthusHex@gmail.com> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240909-arguable-detection-02445bd1cc89@wendy> References: <20240909-arguable-detection-02445bd1cc89@wendy> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2887; i=CoelacanthusHex@gmail.com; h=from:subject; bh=6nGHo0lCtESeld3ret04gh/vnDvSoID5OBGgjnB5oXg=; b=owJ4nJvAy8zAJfY4pvNJRPo6U8bTakkMaQ+cLLeU3+q4sXJjayZnHpd9X/KFC6qHNZ0WLPp3p vaYSqSFeVhHKQuDGBeDrJgii9jOp6+XlT76sIzXZAbMHFYmkCEMXJwCMBGpo4wMCzdbR819rrNh F0PLsqgLuV+EkvbEW2QueDjP0ZO7L/PWcUaGJvErL110T2cvKbabdudw3cITiU0XTzhYze07spC xyuEoLwAho0yn X-Developer-Key: i=CoelacanthusHex@gmail.com; a=openpgp; fpr=892EBC7DC392DFF9C9C03F1D15F4180E73787863 Content-Transfer-Encoding: quoted-printable On 2024-09-09 20:16, Conor Dooley wrote:=0D > On Mon, Sep 09, 2024 at 08:14:16PM +0800, Celeste Liu wrote:=0D > > On 2024-09-09 19:53, Conor Dooley wrote:=0D > > =0D > > > On Fri, Aug 23, 2024 at 01:43:26AM +0800, Celeste Liu wrote:=0D > > >> Commit ba6cfef057e1 ("riscv: enable Docker requirements in defconfig= ")=0D > > >> introduced it because of Docker, but Docker has removed this require= ment=0D > > >> since [1] (2023-04-19).=0D > > >>=0D > > >> For cgroup v1, if turned on, and there's any cgroup in the "cpu" hie= rarchy it=0D > > >> needs an RT budget assigned, otherwise the processes in it will not = be able to=0D > > >> get RT at all. The problem with RT group scheduling is that it requi= res the=0D > > >> budget assigned but there's no way we could assign a default budget,= since the=0D > > >> values to assign are both upper and lower time limits, are absolute,= and need to=0D > > >> be sum up to < 1 for each individal cgroup. That means we cannot rea= lly come up=0D > > >> with values that would work by default in the general case.[2]=0D > > >>=0D > > >> For cgroup v2, it's almost unusable as well. If it turned on, the cp= u controller=0D > > >> can only be enabled when all RT processes are in the root cgroup. Bu= t it will=0D > > >> lose the benefits of cgroup v2 if all RT process were placed in the = same cgroup.=0D > > >>=0D > > >> Red Hat, Gentoo, Arch Linux and Debian all disable it. systemd also = doesn't=0D > > >> support it.[3]=0D > > >>=0D > > >> [1]: https://github.com/moby/moby/commit/005150ed69c540fb0b5323e0f22= 08608c1204536=0D > > >> [2]: https://bugzilla.redhat.com/show_bug.cgi?id=3D1229700=0D > > >> [3]: https://github.com/systemd/systemd/issues/13781#issuecomment-54= 9164383=0D > > >>=0D > > >> Fixes: ba6cfef057e1 ("riscv: enable Docker requirements in defconfig= ")=0D > > > =0D > > > I don't think this fixes tag is suitable, the commit you cite in=0D > > > moby/docker is a year younger than the one in the fixes tag, so it wa= s=0D > > > correct at the time it was written. I think the fixes tag should just= be=0D > > > removed, since that commit was not wrong. Or am I missing something?= =0D > > =0D > > The Docker commit I cited introduce the fix, not the bug. So it should = be later=0D > > than commit in fixes tag, otherwise Heinrich Schuchardt won't pick the = wrong=0D > > config from upstream.=0D > > =0D > > Timeline is:=0D > > 1) 2015-06-19 Qiang Huang introduce RT_GROUP_SCHED check in Docker.[1]= =0D > > 2) 2022-06-08 Heinrich Schuchardt pick this to defconfig in commit=0D > > in fixes tag.=0D > > 3) 2023-04-19 Florian Schmaus remove this requirement from Docker in=0D > > commit I cited.=0D > =0D > Yes, this is the way I understood things to be. IOW, when Heinrich wrote= =0D > ba6cfef057e1 ("riscv: enable Docker requirements in defconfig"), it was=0D > a requirement for docker. The requirement later being removed doesn't=0D > make his patch incorrect, which is why I don't think this is a fix.=0D =0D v3 has been sent.=0D