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Wed, 17 Dec 2025 07:49:10 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.129.40]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-47bd911a9bcsm32202995e9.6.2025.12.17.07.49.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Dec 2025 07:49:09 -0800 (PST) Date: Wed, 17 Dec 2025 16:49:02 +0100 From: Juri Lelli To: Andrea Righi Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Tejun Heo , David Vernet , Changwoo Min , Shuah Khan , Joel Fernandes , Christian Loehle , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 4/7] sched_ext: Add a DL server for sched_ext tasks Message-ID: References: <20251217093923.1556187-1-arighi@nvidia.com> <20251217093923.1556187-5-arighi@nvidia.com> Precedence: bulk X-Mailing-List: bpf@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: <20251217093923.1556187-5-arighi@nvidia.com> Hi! On 17/12/25 10:35, Andrea Righi wrote: > sched_ext currently suffers starvation due to RT. The same workload when > converted to EXT can get zero runtime if RT is 100% running, causing EXT > processes to stall. Fix it by adding a DL server for EXT. ... > v4: - initialize EXT server bandwidth reservation at init time and > always keep it active (Andrea Righi) > - check for rq->nr_running == 1 to determine when to account idle > time (Juri Lelli) > v3: - clarify that fair is not the only dl_server (Juri Lelli) > - remove explicit stop to reduce timer reprogramming overhead > (Juri Lelli) > - do not restart pick_task() when it's invoked by the dl_server > (Tejun Heo) > - depend on CONFIG_SCHED_CLASS_EXT (Andrea Righi) > v2: - drop ->balance() now that pick_task() has an rf argument > (Andrea Righi) > > Tested-by: Christian Loehle > Co-developed-by: Joel Fernandes > Signed-off-by: Joel Fernandes > Signed-off-by: Andrea Righi > --- ... > @@ -3090,6 +3123,15 @@ static void switching_to_scx(struct rq *rq, struct task_struct *p) > static void switched_from_scx(struct rq *rq, struct task_struct *p) > { > scx_disable_task(p); > + > + /* > + * After class switch, if the DL server is still active, restart it so > + * that DL timers will be queued, in case SCX switched to higher class. > + */ > + if (dl_server_active(&rq->ext_server)) { > + dl_server_stop(&rq->ext_server); > + dl_server_start(&rq->ext_server); > + } > } We might have discussed this already, in that case I forgot, sorry. But, why we do need to start the server again if switched from scx? Couldn't make sense of the comment that is already present. Thanks, Juri