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Mon, 21 Jul 2025 02:34:43 -0700 (PDT) From: Yuri Andriaccio To: juri.lelli@redhat.com Cc: bsegall@google.com, dietmar.eggemann@arm.com, linux-kernel@vger.kernel.org, luca.abeni@santannapisa.it, mgorman@suse.de, mingo@redhat.com, peterz@infradead.org, rostedt@goodmis.org, vincent.guittot@linaro.org, vschneid@redhat.com, yurand2000@gmail.com, yuri.andriaccio@santannapisa.it Subject: Re: [BUG] Bw accounting warning on fair-servers' parameters change Date: Mon, 21 Jul 2025 11:34:42 +0200 Message-ID: <20250721093442.244074-1-yurand2000@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Hi, On 18/07/25 16:53, Juri Lelli wrote: > On 18/07/25 16:22, Juri Lelli wrote: > > Hi, > > > > Thanks for reporting. > > > > On 18/07/25 13:38, Yuri Andriaccio wrote: > > > Hi, > > > > > > I've been lately working on fair-servers and dl_servers for some patches and > > > I've come across a bandwidth accounting warning on the latest tip/master (as of > > > 2025-07-18, git sha ed0272f0675f). The warning is triggered by simply starting > > > the machine, mounting debugfs and then just zeroing any fair-server's runtime. > > > > > > > > > The warning: > > > > > > WARNING: kernel/sched/deadline.c:266 at dl_rq_change_utilization+0x208/0x230 > > > static inline void __sub_rq_bw(u64 dl_bw, struct dl_rq *dl_rq) { > > > ... > > > WARN_ON_ONCE(dl_rq->running_bw > dl_rq->this_bw); > > > } > > > > > > Steps to reproduce: > > > > > > mount -t debugfs none /sys/kernel/debug > > > echo 0 > /sys/kernel/debug/sched/fair_server/cpu0/runtime > > > > > > > > > It does not happen at every machine boot, but happens on most. Could it possibly > > > be related to some of the deadline timers? > > > > I took a quick first look and currently suspect cccb45d7c4295 > > ("sched/deadline: Less agressive dl_server handling") could be playing a > > role in this as it delays actual server stop. > > > > Could you please try to repro after having reverted such commit? > > After that (w/o the revert), could you please try to see if the > following helps? I've been performing some tests as you asked and indeed the culprit seems to be cccb45d7c4295 ("sched/deadline: Less agressive dl_server handling"), as reverting it on the current tip removes the issue. I've also tested the fix you posted (w/o the reverted commit), and I can confirm that the warning does not seem to be triggered anymore. Thanks, Yuri