From nobody Wed Feb 11 06:30:43 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6EC92C7EE23 for ; Thu, 8 Jun 2023 16:00:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237573AbjFHP7Z (ORCPT ); Thu, 8 Jun 2023 11:59:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47406 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237577AbjFHP65 (ORCPT ); Thu, 8 Jun 2023 11:58:57 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9D0F211A for ; Thu, 8 Jun 2023 08:58:52 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 37B8764EC6 for ; Thu, 8 Jun 2023 15:58:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDBC5C433D2; Thu, 8 Jun 2023 15:58:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1686239931; bh=WAjW/aFhAStD3otQ1mS7pNSbSHMBmtJIFN275Bic5kM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=d+O9GR1cnStXZVNONXFwv51PLpkZMfpBoC2XCXzOv8Nz3FT8NXr3VOi4mbUMpaPRD OWwS8wLjRSZT5ZpdeuoU/hd8jjATLEQXPVBVpSwxdYaAT3ViTTuLDQc5+PO8vYSVd+ n8VTlKuphSndp5t/abhf4nsJZMmKRQl/YB3aaVpMATWzYiJGTONIMDQAZoakCQtpiU Trw2MxQNJ2BXHUiVzApTftjAUX3bFFXpwQlp9iNAo5RwTNUHcLjd7XhqRegSrbpFGz vHGAxo8aHBefnSbQ/fr7liQTLde5MzJLXqmiU5X1L1VYrpYzjczFhmsHwt7oyaGjLg KugfnIT/Hsvog== From: Daniel Bristot de Oliveira To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot Cc: Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org, Luca Abeni , Tommaso Cucinotta , Thomas Gleixner , Joel Fernandes , Vineeth Pillai , Shuah Khan , Daniel Bristot de Oliveira Subject: [RFC PATCH V3 5/6] sched/fair: Add trivial fair server Date: Thu, 8 Jun 2023 17:58:17 +0200 Message-Id: <8db5a49ea92ad8b875d331d6136721645a382fe8.1686239016.git.bristot@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Peter Zijlstra Use deadline servers to service fair tasks. This patch adds a fair_server deadline entity which acts as a container for fair entities and can be used to fix starvation when higher priority (wrt fair) tasks are monopolizing CPU(s). Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Daniel Bristot de Oliveira --- kernel/sched/core.c | 1 + kernel/sched/fair.c | 29 +++++++++++++++++++++++++++++ kernel/sched/sched.h | 4 ++++ 3 files changed, 34 insertions(+) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 5b88b822ec89..7506dde9849d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10058,6 +10058,7 @@ void __init sched_init(void) #endif /* CONFIG_SMP */ hrtick_rq_init(rq); atomic_set(&rq->nr_iowait, 0); + fair_server_init(rq); =20 #ifdef CONFIG_SCHED_CORE rq->core =3D rq; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 0c58d8e55b69..f493f05c1f84 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6336,6 +6336,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *= p, int flags) */ util_est_enqueue(&rq->cfs, p); =20 + if (!rq->cfs.h_nr_running) + dl_server_start(&rq->fair_server); + /* * If in_iowait is set, the code below may not trigger any cpufreq * utilization updates, so do it here explicitly with the IOWAIT flag @@ -6480,6 +6483,9 @@ static void dequeue_task_fair(struct rq *rq, struct t= ask_struct *p, int flags) rq->next_balance =3D jiffies; =20 dequeue_throttle: + if (!rq->cfs.h_nr_running) + dl_server_stop(&rq->fair_server); + util_est_update(&rq->cfs, p, task_sleep); hrtick_update(rq); } @@ -8221,6 +8227,29 @@ static struct task_struct *__pick_next_task_fair(str= uct rq *rq) return pick_next_task_fair(rq, NULL, NULL); } =20 +static bool fair_server_has_tasks(struct sched_dl_entity *dl_se) +{ + return !!dl_se->rq->cfs.nr_running; +} + +static struct task_struct *fair_server_pick(struct sched_dl_entity *dl_se) +{ + return pick_next_task_fair(dl_se->rq, NULL, NULL); +} + +void fair_server_init(struct rq *rq) +{ + struct sched_dl_entity *dl_se =3D &rq->fair_server; + + init_dl_entity(dl_se); + + dl_se->dl_runtime =3D TICK_NSEC; + dl_se->dl_deadline =3D 20 * TICK_NSEC; + dl_se->dl_period =3D 20 * TICK_NSEC; + + dl_server_init(dl_se, rq, fair_server_has_tasks, fair_server_pick); +} + /* * Account for a descheduled task: */ diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 390c99e2f8a8..d4a7c0823c53 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -353,6 +353,8 @@ extern void dl_server_init(struct sched_dl_entity *dl_s= e, struct rq *rq, dl_server_has_tasks_f has_tasks, dl_server_pick_f pick); =20 +extern void fair_server_init(struct rq *); + #ifdef CONFIG_CGROUP_SCHED =20 struct cfs_rq; @@ -1015,6 +1017,8 @@ struct rq { struct rt_rq rt; struct dl_rq dl; =20 + struct sched_dl_entity fair_server; + #ifdef CONFIG_FAIR_GROUP_SCHED /* list of leaf cfs_rq on this CPU: */ struct list_head leaf_cfs_rq_list; --=20 2.40.1