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Wed, 17 Dec 2025 23:14:15 -0800 (PST) Received: from jlelli-thinkpadt14gen4.remote.csb ([151.29.129.40]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4324493fe27sm3248198f8f.12.2025.12.17.23.14.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Dec 2025 23:14:15 -0800 (PST) Date: Thu, 18 Dec 2025 08:14:13 +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 v2 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: linux-kselftest@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: Hi! On 17/12/25 22:55, 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. > > A kselftest is also included later to confirm that both DL servers are > functioning correctly: > > # ./runner -t rt_stall > ===== START ===== > TEST: rt_stall > DESCRIPTION: Verify that RT tasks cannot stall SCHED_EXT tasks > OUTPUT: > TAP version 13 > 1..1 > # Runtime of FAIR task (PID 1511) is 0.250000 seconds > # Runtime of RT task (PID 1512) is 4.750000 seconds > # FAIR task got 5.00% of total runtime > ok 1 PASS: FAIR task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of EXT task (PID 1514) is 0.250000 seconds > # Runtime of RT task (PID 1515) is 4.750000 seconds > # EXT task got 5.00% of total runtime > ok 2 PASS: EXT task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of FAIR task (PID 1517) is 0.250000 seconds > # Runtime of RT task (PID 1518) is 4.750000 seconds > # FAIR task got 5.00% of total runtime > ok 3 PASS: FAIR task got more than 4.00% of runtime > TAP version 13 > 1..1 > # Runtime of EXT task (PID 1521) is 0.250000 seconds > # Runtime of RT task (PID 1522) is 4.750000 seconds > # EXT task got 5.00% of total runtime > ok 4 PASS: EXT task got more than 4.00% of runtime > ok 1 rt_stall # > ===== END ===== > > v5: - do not restart the EXT server on switch_class() (Juri Lelli) > 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 > --- This new version looks good to me, thanks! Reviewed-by: Juri Lelli Best, Juri