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Thu, 12 Nov 2026 16:16:41 +0000 From: Fernand Sieber To: Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , Shuah Khan CC: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Daniel Bristot de Oliveira , Joel Fernandes , Josh Don , , , , Fahad Mubeen , "David Woodhouse" , Misha Karataiev , Hendrik Borghorst , Ibrahim Elshahed , Fernand Sieber Subject: [PATCH 2/5] sched/core: Keep a sibling's DL server link in the core-wide pick Date: Thu, 12 Nov 2026 18:15:45 +0200 Message-ID: <20261112161548.78189-3-sieberf@amazon.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261112161548.78189-1-sieberf@amazon.com> References: <20261112161548.78189-1-sieberf@amazon.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 X-ClientProxiedBy: EX19D031UWA002.ant.amazon.com (10.13.139.96) To EX19D001UWA001.ant.amazon.com (10.13.138.214) Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit The core-wide selection records in rq_i->core_dl_server the DL server each sibling's pick came through, then clears it for every sibling in the cookie matching loop, including when the pick is kept. The sibling takes the fast path, which sets rq->dl_server from rq->core_dl_server, and runs the task its server picked with p->dl_server NULL. Only the selecting CPU keeps the link, as its pick goes through rq->dl_server. A running task is ranked for core scheduling by p->dl_server. While such a task runs on a sibling, each following core-wide selection ranks it as a plain fair or ext task rather than by its server's deadline, so a higher class task on another sibling takes the core back before the server's runtime is used. The RV nomiss monitor, which follows the server through next->dl_server at sched_switch, does not see the server run either. Keep the server that pick_task() left in rq_i->dl_server. With the previous patch it is NULL when the class pick was replaced. Drop the assignment in the first loop, which the matching loop always overwrites. Fixes: bd9bbc96e835 ("sched: Rework dl_server") Signed-off-by: Fernand Sieber --- kernel/sched/core.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f7ac13186ee59..61d4e6e990bba 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6431,7 +6431,6 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) } rq_i->core_pick = p; - rq_i->core_dl_server = rq_i->dl_server; if (!max || prio_less(max, p, fi_before)) max = p; @@ -6462,7 +6461,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) } rq_i->core_pick = p; - rq_i->core_dl_server = NULL; + rq_i->core_dl_server = rq_i->dl_server; if (p == rq_i->idle) { if (rq_i->nr_running) { -- 2.47.3 Amazon Development Centre (South Africa) (Proprietary) Limited 29 Gogosoa Street, Observatory, Cape Town, Western Cape, 7925, South Africa Registration Number: 2004 / 034463 / 07