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[80.47.6.60]) by smtp.gmail.com with ESMTPSA id af79cd13be357-87772460a54sm168528585a.18.2025.10.02.02.00.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 02 Oct 2025 02:00:29 -0700 (PDT) Date: Thu, 2 Oct 2025 10:00:24 +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 v3 00/24] Hierarchical Constant Bandwidth Server Message-ID: References: <20250929092221.10947-1-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: <20250929092221.10947-1-yurand2000@gmail.com> Hello! On 29/09/25 11:21, Yuri Andriaccio wrote: > Hello, > > This is the v3 for Hierarchical Constant Bandwidth Server, aiming at replacing > the current RT_GROUP_SCHED mechanism with something more robust and > theoretically sound. The patchset has been presented at OSPM25 > (https://retis.sssup.it/ospm-summit/), and a summary of its inner workings can > be found at https://lwn.net/Articles/1021332/ . You can find the previous > versions of this patchset at the bottom of the page, in particular version 1 > which talks in more detail what this patchset is all about and how it is > implemented. > > This v3 version further reworks some of the patches as suggested by Juri Lelli. > While most of the work is refactorings, the following were also changed: > - The first patch which removed fair-servers' bandwidth accounting has been > removed, as it was deemed wrong. You can find the last version of this removed > patch, just for history reasons, here: > https://lore.kernel.org/all/20250903114448.664452-1-yurand2000@gmail.com/ Peter wasn't indeed happy with that patch, but I am not sure we finished that discussion. Both myself and Luca had further objections to what Peter said, but not further replies after (which can very well be a sign that he is still adamnt in saying no go away :). Peter? https://lore.kernel.org/lkml/aLk9BNnFYZ3bhVAE@jlelli-thinkpadt14gen4.remote.csb/ https://lore.kernel.org/lkml/20250904091217.78de3dde@luca64/ ... > For this v3 version we've also polished the testing system we are using and made > it public for testers to run on their own machines. The source code can be found > at https://github.com/Yurand2000/HCBS-Test-Suite , along with a README that > explains how to use it. Nonetheless I've reported a description of the tools and > instruction later in the page. Thanks for this. Quite cool. I tried to run the tests, but it looks like the migration set brought my qemu 8 CPUs system to an halt (had to kill the thing). I will try again. I have been working a bit in trying to come up with a testing framework for SCHED_DEADLINE, which I didn't unfortunately posted yet mostly because I was waiting for the discussion about the patch mentioned above to settle (which would require adaptation in the tests that check for bandwidth limits). You can find the idea here [1]. It's thought to be an addition to kselftests. I believe your test suite can be extended to cover the tests I implemented and more, so I am not super attached to my attempt, but it would be good (I think) to converge to something that we can maintain for the future, so maybe have a plan to possibly merge the suites. What do you think? 1 - https://github.com/jlelli/linux/commits/experimental/deadline-selftests-scripts/ ... > Testing v3: > > The HCBS mechanism has been evaluated on several syntetic tests which are > designed to stress the HCBS scheduler and verify that non-interference and > mathematical schedulability guarantees are really enforced by the scheduling > algorithm. ... > The tasksets minimal requirements were computed using a closed-source software, > explaining why the tasksets are supplied separately. A open-source analyser is > being written to update this step in the future and also allow for more > customization for the testers. On this (generation of random taskset and corresponding schedulability checks) I also started working on a different tool, rt-audit. https://github.com/jlelli/rt-audit It's very simple, the tool, the random generation and the checks. But I honestly like the idea that it's based on rt-app. Please take a look if you have a chance and tell me what you think. Again, I feel it would be good to converge towards something open that we can maintain. I will be trying to find time to continue testing and reviewing this RFC of course. Thanks, Juri