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Mon, 21 Jul 2025 06:35:37 -0700 (PDT) X-Google-Smtp-Source: AGHT+IGKLxevCXAp/ZaKcZG6IGYm2011Dp/msW7/oCb3X6AMF1wQkf7r2hLAjijhWGwIYKj/zf1bMQ== X-Received: by 2002:a05:6000:40cc:b0:3b5:f0aa:b1e5 with SMTP id ffacd0b85a97d-3b60e4c21aamr14987236f8f.19.1753104937432; Mon, 21 Jul 2025 06:35:37 -0700 (PDT) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.54.209]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4562e7f4289sm160704865e9.7.2025.07.21.06.35.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Jul 2025 06:35:36 -0700 (PDT) Date: Mon, 21 Jul 2025 15:35:34 +0200 From: Juri Lelli To: Yuri Andriaccio 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, yuri.andriaccio@santannapisa.it Subject: Re: [BUG] Bw accounting warning on fair-servers' parameters change Message-ID: References: <20250721093442.244074-1-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: <20250721093442.244074-1-yurand2000@gmail.com> On 21/07/25 11:34, Yuri Andriaccio wrote: > 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! Sent out a clean-up version https://lore.kernel.org/lkml/20250721-upstream-fix-dlserver-lessaggressive-b4-v1-1-4ebc10c87e40@redhat.com/