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Mon, 17 Feb 2025 06:52:17 -0800 (PST) X-Google-Smtp-Source: AGHT+IHTVdSBHOISJ5tDzp41H2vIhrlfxz3GOda5fRJNmab4HtNRj85X8u3+oM45gnUlcyd4iGxLMA== X-Received: by 2002:adf:e387:0:b0:38f:2113:fba0 with SMTP id ffacd0b85a97d-38f34171386mr7355505f8f.50.1739803937339; Mon, 17 Feb 2025 06:52:17 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.34.42]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f2580fe7dsm12482708f8f.0.2025.02.17.06.52.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Feb 2025 06:52:16 -0800 (PST) Date: Mon, 17 Feb 2025 15:52:14 +0100 From: Juri Lelli To: Qais Yousef Cc: Dietmar Eggemann , Christian Loehle , Jon Hunter , Thierry Reding , Waiman Long , Tejun Heo , Johannes Weiner , Michal Koutny , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Phil Auld , Sebastian Andrzej Siewior , "Joel Fernandes (Google)" , Suleiman Souhlal , Aashish Sharma , Shin Kawamura , Vineeth Remanan Pillai , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, "linux-tegra@vger.kernel.org" Subject: Re: [PATCH v2 3/2] sched/deadline: Check bandwidth overflow earlier for hotplug Message-ID: References: <5a36a2e8-bd78-4875-9b9e-814468ca6692@arm.com> <8ff19556-a656-4f11-a10c-6f9b92ec9cea@arm.com> <285a43db-c36d-400e-8041-0566f089a482@arm.com> <20250216163340.ttwddti5pzuynsj5@airbuntu> Precedence: bulk X-Mailing-List: linux-tegra@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: <20250216163340.ttwddti5pzuynsj5@airbuntu> On 16/02/25 16:33, Qais Yousef wrote: > On 02/13/25 07:20, Juri Lelli wrote: > > On 12/02/25 19:22, Dietmar Eggemann wrote: > > > On 11/02/2025 11:42, Juri Lelli wrote: > > > > ... > > > > > > What about we actually ignore them consistently? We already do that for > > > > admission control, so maybe we can do that when rebuilding domains as > > > > well (until we find maybe a better way to deal with them). > > > > > > > > Does the following make any difference? > > > > > > It at least seems to solve the issue. And like you mentioned on irc, we > > > don't know the bw req of sugov anyway. > > > > > > So with this change we start with 'dl_bw->total_bw = 0' even w/ sugov tasks. > > > > > > dl_rq[0]: > > > .dl_nr_running : 0 > > > .dl_bw->bw : 996147 > > > .dl_bw->total_bw : 0 <-- ! > > > > > > IMHO, people who want to run serious DL can always check whether there > > > are already these infrastructural DL tasks or even avoid schedutil. > > > > It definitely not ideal and admittedly gross, but not worse than what we > > are doing already considering we ignore sugovs at AC and the current > > bandwidth allocation its there only to help with PI. So, duck tape. :/ > > > > A more proper way to work with this would entail coming up with sensible > > bandwidth allocation for sugovs, but that's most probably hardware > > specific, so I am not sure how we can make that general enough. > > I haven't been following the problem closely, but one thing I was considering > and I don't know if it makes sense to you and could help with this problem too. > Shall we lump sugov with stopper class or create a new sched_class (seems > unnecessary, I think stopper should do)? With the consolidate cpufreq update > patch I've been working on Vincent raised issues with potential new ctx switch > and to improve that I needed to look at improving sugov wakeup path. If we > decouple it from DL I think that might fix your problem here and could allow us > to special case it for other problems like the ones I faced more easily without > missing up with DL. > > Has the time come to consider retire the simple solution of making sugov a fake > DL task? Problem is that 'ideally' we would want to explicitly take sugovs into account when designing the system. We don't do that currently as a 'temporary solution' that seemed simpler than a proper approach (started wondering if it's indeed simpler). So, not sure if moving sugovs outside DL is something we want to do. Thanks, Juri