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Thu, 09 Oct 2025 06:54:09 -0700 (PDT) X-Google-Smtp-Source: AGHT+IFQ/8MsxFrzKCmHq5d4yjkcV7RwIUXvn1VDs8nPuEzaq9UOMUEaZcxzNaixtyucoW6t9PGXSA== X-Received: by 2002:a05:6000:26d1:b0:3fa:2df7:6a0a with SMTP id ffacd0b85a97d-425829ee53emr7408946f8f.22.1760018048952; Thu, 09 Oct 2025 06:54:08 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.13.103]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46faf11197esm51253935e9.6.2025.10.09.06.54.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 09 Oct 2025 06:54:08 -0700 (PDT) Date: Thu, 9 Oct 2025 15:54:06 +0200 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 v3 14/24] sched/rt: Allow zeroing the runtime of the root control group Message-ID: References: <20250929092221.10947-1-yurand2000@gmail.com> <20250929092221.10947-15-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: <20250929092221.10947-15-yurand2000@gmail.com> Hello, On 29/09/25 11:22, 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 bandwdith ^ 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), buy they ^ but > 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 > --- Thanks, Juri