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Wed, 21 Jan 2026 02:32:47 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.129.40]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4801e8795f1sm305997735e9.6.2026.01.21.02.32.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 Jan 2026 02:32:45 -0800 (PST) Date: Wed, 21 Jan 2026 11:32:44 +0100 From: Juri Lelli To: Yuri Andriaccio Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org, Luca Abeni , Yuri Andriaccio Subject: Re: [RFC PATCH v4 15/28] sched/rt: Allow zeroing the runtime of the root control group Message-ID: References: <20251201124205.11169-1-yurand2000@gmail.com> <20251201124205.11169-16-yurand2000@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251201124205.11169-16-yurand2000@gmail.com> Hello, On 01/12/25 13:41, Yuri Andriaccio wrote: > In HCBS, the root control group follows the already existing rules for > rt-task scheduling. As such, it does not make use of the deadline servers > to account for runtime, or any other HCBS specific code and features. > > While the runtime of SCHED_DEADLINE tasks depends on the global bandwidth > reserved for rt_tasks, the runtime of SCHED_FIFO/SCHED_RR tasks is limited > by the activation of fair-servers (as the RT_THROTTLING mechanism has been > removed in favour of them), thus their maximum bandwidth depends solely on > the fair-server settings (which are thightly related to the global > bandwidth reserved for rt-tasks) and the amount of SCHED_OTHER workload to > run (recall that if no SCHED_OTHER tasks are running, the FIFO/RR tasks > may fully utilize the CPU). > > The values of runtime and period in the root cgroup's cpu controller do > not affect, by design of HCBS, the fair-server settings and similar > (consequently they do not affect the scheduling of FIFO/RR tasks in the > root cgroup), but they are just used to reserve a portion of the > SCHED_DEADLINE bandwidth to the scheduling of rt-cgroups. These values > only affect child cgroups, their deadline servers and their assigned > FIFO/RR tasks. > > Signed-off-by: Yuri Andriaccio Reviewed-by: Juri Lelli Thanks, Juri