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Fri, 13 Nov 2026 07:57:34 -0800 (PST) X-Received: by 2002:a05:6000:2613:b0:48e:3085:7cf0 with SMTP id ffacd0b85a97d-49c7467b551mr5465726f8f.51.1794585453647; Fri, 13 Nov 2026 07:57:33 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.158.90]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-49c60116323sm5776550f8f.32.2026.11.13.07.57.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2026 07:57:32 -0800 (PST) Date: Fri, 13 Nov 2026 16:57:29 +0100 From: Juri Lelli To: Mathieu Desnoyers Cc: peterz@infradead.org, mingo@redhat.com, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, tglx@kernel.org, will@kernel.org, boqun@kernel.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, luca.abeni@santannapisa.it, mathieu.poirier@linaro.org, longman@redhat.com, ridong.chen@linux.dev, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, shuah@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, parri.andrea@gmail.com, m.szyprowski@samsung.com, kayracizmeci@gmail.com, weihengqiuu@gmail.com, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-rt-devel@lists.linux.dev, stable@vger.kernel.org Subject: Re: [PATCH v5 20/29] cgroup/cpuset: Give back the bandwidth an attach did not move Message-ID: References: <20261108185406.1549770-1-mathieu.desnoyers@efficios.com> <20261108185406.1549770-21-mathieu.desnoyers@efficios.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On 13/11/26 08:12, Mathieu Desnoyers wrote: ... > Three new patches keep a deadline task in the root domain that counts > its bandwidth: > - Where a CPU is picked for the task, a CPU of that root domain is > tried first. This covers a CPU offline, a mask change, a wakeup and > a rebuild. > - A CPU offline fails with EBUSY if it takes the last CPU the task has > in that root domain. > - A write to cpuset.cpus fails with EBUSY if it leaves the task no CPU > in that root domain. cpuset makes a partition root that would do the > same invalid. Makes sense to me. > The bandwidth of a task then goes to another root domain only by a > cpuset attach, which asks for room. > > With admission control off, nothing is refused, and patch 23 still > moves the bandwidth. So an administrator gets past a refusal by writing > -1 to sched_rt_runtime_us. The two refusals are new behaviour for > user-space. I would like your opinion on them, and on whether that knob > is enough or a dedicated one is wanted. I believe we already have (maybe broken in-kernel) EBUSY on trying to hotplug last cpu with bw standing? About a potential dedicate knob, Sebastian is proposing it as well [1], so maybe it's time we move to that. Need to sync with him I guess. :) Thanks, Juri 1 - https://lore.kernel.org/lkml/20261113-sched_dl-v3-5-a76ffa1cdeee@linutronix.de/