From nobody Fri Sep 25 07:23:39 2026 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3FCFE41CB4D for ; Tue, 15 Sep 2026 16:33:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.5 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789489991; cv=none; b=W5JLMWiA1VQO66NA+4ygtdRRIVEGKvZ5dZafNMRd1ko3mAm4jwAy7/J18IVXbHBHvCasa5W7nzB9SAFaO0yn0nKxrQmvcqcRqRDdicgZmQxfvoRxZQhyWr521IkCGGVWG3KrOUrXVPyx9egGCg+Ba/AjeHVb+iKI9WCxMSV+ISk= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789489991; c=relaxed/simple; bh=JIhc4E+BK6Mnyvy+z+2XlIMF9YN8CD6pk246LNxI4Ac=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=numBletL0b85dVpJvBp/bvhikq8jB3Zjd6h+bV2eaYijswOwMrai4GhUB/jGTRXBbGxostStlx1bi9WiZ3vKZ+IO8easj6zsjahtBgaMp7cb/TNv0Jth+tUyWo45PcbEU25RH/HoyNKpw5pOHhZHvcIkz8dJX4iEps5+Pt3dJpY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=RCQU+e2I; arc=none smtp.client-ip=220.197.31.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="RCQU+e2I" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=Ma dzqak28alg5GHoSvVFd2+TBIkVYYme5MOU9NZ3gyo=; b=RCQU+e2IVGoQYRwM1d Jx1LjoyDPq+zO0uz4BdJQZfjb6o3vAwMf0FfVYGtXCLJdEmdzEJTVwFJNX4cSku+ dmI4rXyxpzlrsL9wUbMEwSmHoSDm+P29Yc8MypekJxYZzcoIXcyT9E8RoNUo+KqB E002LUyjpnZDBAPOPe+ak/3+0= Received: from localhost (unknown []) by gzga-smtp-mtada-g0-1 (Coremail) with SMTP id _____wAHWt7qcqlqqrxdAw--.59678S2; Wed, 16 Sep 2026 00:31:39 +0800 (CST) From: Hui Su To: peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org Subject: [PATCH] sched/core: Remove redundant core_sched_seq Date: Wed, 16 Sep 2026 01:31:38 +0900 Message-ID: <20260915163138.2973969-1-sh_def@163.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: _____wAHWt7qcqlqqrxdAw--.59678S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxGF17ZryfKw4fGw1DtryDGFg_yoW5Kr1xpr 9rJ3yDJ3WDKF1Utr1rZw4xGrWUGwn5A343WrnxXayIkF1rGrWFqr1vgw12vrWqkr4q9a42 yFsIg39FqrZruaDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07UDMa5UUUUU= X-CM-SenderInfo: xvkbvvri6rljoofrz/xtbCwgvbO2qpcutkbAAA37 Content-Type: text/plain; charset="utf-8" core_sched_seq records whether an rq has consumed the pick made by the last core-wide selection. However, rq->core_pick already carries the same per-rq state. A core-wide selection leaves core_pick populated only for siblings which still need to consume their picks. It is cleared when the current CPU consumes its pick, when a sibling is already running the selected task, or when a pending pick is consumed through the fastpath. The CPU offline path clears it as well. core_task_seq and core_pick_seq serve a separate purpose. core_task_seq changes when the task set changes and for each new core-wide pick, while core_pick_seq records the task sequence on which the selection was made. Their equality therefore establishes that a pending core_pick is still valid. Consequently, once core_pick_seq =3D=3D core_task_seq, a non-NULL core_pick= is sufficient to tell that this rq still has a pick to consume. core_sched_seq duplicates that pending/consumed state. Remove core_sched_seq and use core_pick directly as the pending marker. Testing included an instrumented comparison of the old and new pending predicates under core-scheduling stress. Additional guest tests exercised repeated core-cookie lifecycles, forced idle, and CPU hotplug under load. No predicate divergence or kernel warning was observed. Signed-off-by: Hui Su --- kernel/sched/core.c | 10 ++++------ kernel/sched/sched.h | 1 - 2 files changed, 4 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7885ff76e69f..6025d37532c6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6276,10 +6276,7 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) * selection. In this case, do a core-wide selection. */ if (rq->core->core_pick_seq =3D=3D rq->core->core_task_seq && - rq->core->core_pick_seq !=3D rq->core_sched_seq && rq->core_pick) { - WRITE_ONCE(rq->core_sched_seq, rq->core->core_pick_seq); - next =3D rq->core_pick; rq->dl_server =3D rq->core_dl_server; rq->core_pick =3D NULL; @@ -6311,11 +6308,13 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) } =20 /* - * core->core_task_seq, core->core_pick_seq, rq->core_sched_seq + * core->core_task_seq, core->core_pick_seq * * @task_seq guards the task state ({en,de}queues) * @pick_seq is the @task_seq we did a selection on - * @sched_seq is the @pick_seq we scheduled + * + * Once a core-wide selection is committed, a non-NULL core_pick denotes + * a pick which still needs to be consumed on this CPU. * * However, preemptions can cause multiple picks on the same task set. * 'Fix' this by also increasing @task_seq for every pick. @@ -6422,7 +6421,6 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) =20 rq->core->core_pick_seq =3D rq->core->core_task_seq; next =3D rq->core_pick; - rq->core_sched_seq =3D rq->core->core_pick_seq; =20 /* Something should have been selected for current CPU */ WARN_ON_ONCE(!next); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index e656c7059bf8..d1441bf6b4ef 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1371,7 +1371,6 @@ struct rq { struct task_struct *core_pick; struct sched_dl_entity *core_dl_server; unsigned int core_enabled; - unsigned int core_sched_seq; struct rb_root core_tree; =20 /* shared state -- careful with sched_core_cpu_deactivate() */ base-commit: 587858367581b9c55c3690f4e63382ad622719d4 --=20 2.55.0