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Tue, 21 Apr 2026 23:33:08 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([176.206.7.99]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48a55b8baaesm160969155e9.10.2026.04.21.23.33.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Apr 2026 23:33:08 -0700 (PDT) Date: Wed, 22 Apr 2026 08:33:05 +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: [PATCH] sched/deadline: Fix replenishment logic for non-deferred servers Message-ID: References: <20260420163410.20808-1-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: <20260420163410.20808-1-yurand2000@gmail.com> Hi Yuri, On 20/04/26 18:34, Yuri Andriaccio wrote: > A special flag of the deadline entities, the 'dl_defer' flag, is explicitly > documents changing the behaviour of deadline tasks and servers to the special > deferred behaviour that replenishes and unthrottles the linked dl entity just in > time so it does not miss its deadline. Maybe rephrase to make it more direct, like "The dl_defer flag is used ..."? > Currently, this behaviour is only used by fair-servers (and ext-servers), while > regular tasks use the original CBS (Constant Bandwidth Server) rules. > > The bug (and fix) which follows is of interest to those deadline server entities > which do not request the deferred behaviour (i.e., dl_defer = 0): > whenever a non-deferred deadline entity expends all of its runtime it must start > the replenishment timer or, if the wake-up instant is too close to the current > time, the entity must be simply re-enqueued and its runtime replenished. > Currently, the 'dl_defer' flag is ignored when replenishing any deadline server, > defaulting to the deferred behaviour, while this fix correctly addresses the > issue. I think we might want to make the above more imperative (don't use "this fix", etc). Simply state what the fix does. > Unfortunately, no testing of this bugfix is possible as there are currently no > deadline servers which use the standard non-deferred behaviour. This bug was > discovered during the development of the Hierarchical CBS patch > (https://lore.kernel.org/all/20251201124205.11169-1-yurand2000@gmail.com/) which > makes extensive use of the non-deferred servers. > > Thanks for your support and have a nice day, > Yuri The above (from "Unfortunately..) doesn't belong to the changelog, you can put it under the --- region in your next version if you want to add comments of this type. > Signed-off-by: Yuri Andriaccio > --- Apart from the suggestions above, the fix makes sense to me (and I trust it works with the rest of HCBS patches you are working on). Thanks! Juri