From nobody Sat Feb 7 17:19:43 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 CF025EB64D8 for ; Thu, 22 Jun 2023 13:28:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230243AbjFVN2x (ORCPT ); Thu, 22 Jun 2023 09:28:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39978 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230355AbjFVN2v (ORCPT ); Thu, 22 Jun 2023 09:28:51 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 395FC1997 for ; Thu, 22 Jun 2023 06:28:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1687440487; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=m0MsYlp7FICmkkjzEoJpY6Zv2dtdWzKtFpA83D/IL1A=; b=CMY07IHOQ1il/kP8KGNAPqV8B95XOs/BF3ykHdXhq5hUNkVnmL3xpG0ts+UZMP0HSZZ5oG o2T3SjDTcvDMGCmRbddCumLhIPP8+gNBREd22cnyKb7BVn8B+jji6WLZ3Lx7MplQSuLqyN xMYL75eKIFOTAlj44bFZ0xuhYS5kgBs= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-483-AjFBXJlnPoW1hXfIwXoWBQ-1; Thu, 22 Jun 2023 09:28:02 -0400 X-MC-Unique: AjFBXJlnPoW1hXfIwXoWBQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 09DE338117E3; Thu, 22 Jun 2023 13:27:53 +0000 (UTC) Received: from pauld.bos.com (dhcp-17-165.bos.redhat.com [10.18.17.165]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8F5F9200B402; Thu, 22 Jun 2023 13:27:52 +0000 (UTC) From: Phil Auld To: linux-kernel@vger.kernel.org Cc: Juri Lelli , Ingo Molnar , Daniel Bristot de Oliveira , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Ben Segall , Steven Rostedt , Mel Gorman , Phil Auld Subject: [PATCH] Sched/fair: Block nohz tick_stop when cfs bandwidth in use Date: Thu, 22 Jun 2023 09:27:51 -0400 Message-Id: <20230622132751.2900081-1-pauld@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" CFS bandwidth limits and NOHZ full don't play well together. Tasks can easily run well past their quotas before a remote tick does accounting. This leads to long, multi-period stalls before such tasks can run again. Currentlyi, when presented with these conflicting requirements the scheduler is favoring nohz_full and letting the tick be stopped. However, nohz tick stopping is already best-effort, there are a number of conditions that can prevent it, whereas cfs runtime bandwidth is expected to be enforced. Make the scheduler favor bandwidth over stopping the tick by setting TICK_DEP_BIT_SCHED when the only running task is a cfs task with runtime limit enabled. Add sched_feat HZ_BW (off by default) to control this behavior. Signed-off-by: Phil Auld Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Vincent Guittot Cc: Juri Lelli Cc: Dietmar Eggemann Cc: Valentin Schneider Cc: Ben Segall --- kernel/sched/fair.c | 33 ++++++++++++++++++++++++++++++++- kernel/sched/features.h | 2 ++ 2 files changed, 34 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 373ff5f55884..880eadfac330 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6139,6 +6139,33 @@ static void __maybe_unused unthrottle_offline_cfs_rq= s(struct rq *rq) rcu_read_unlock(); } =20 +#ifdef CONFIG_NO_HZ_FULL +/* called from pick_next_task_fair() */ +static void sched_fair_update_stop_tick(struct rq *rq, struct task_struct = *p) +{ + struct cfs_rq *cfs_rq =3D task_cfs_rq(p); + int cpu =3D cpu_of(rq); + + if (!sched_feat(HZ_BW) || !cfs_bandwidth_used()) + return; + + if (!tick_nohz_full_cpu(cpu)) + return; + + if (rq->nr_running !=3D 1 || !sched_can_stop_tick(rq)) + return; + + /* + * We know there is only one task runnable and we've just picked it. The + * normal enqueue path will have cleared TICK_DEP_BIT_SCHED if we will + * be otherwise able to stop the tick. Just need to check if we are using + * bandwidth control. + */ + if (cfs_rq->runtime_enabled) + tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED); +} +#endif + #else /* CONFIG_CFS_BANDWIDTH */ =20 static inline bool cfs_bandwidth_used(void) @@ -6181,9 +6208,12 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth= (struct task_group *tg) static inline void destroy_cfs_bandwidth(struct cfs_bandwidth *cfs_b) {} static inline void update_runtime_enabled(struct rq *rq) {} static inline void unthrottle_offline_cfs_rqs(struct rq *rq) {} - #endif /* CONFIG_CFS_BANDWIDTH */ =20 +#if !defined(CONFIG_CFS_BANDWIDTH) || !defined(CONFIG_NO_HZ_FULL) +static inline void sched_fair_update_stop_tick(struct rq *rq, struct task_= struct *p) {} +#endif + /************************************************** * CFS operations on tasks: */ @@ -8097,6 +8127,7 @@ done: __maybe_unused; hrtick_start_fair(rq, p); =20 update_misfit_status(p, rq); + sched_fair_update_stop_tick(rq, p); =20 return p; =20 diff --git a/kernel/sched/features.h b/kernel/sched/features.h index ee7f23c76bd3..6fdf1fdf6b17 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -101,3 +101,5 @@ SCHED_FEAT(LATENCY_WARN, false) =20 SCHED_FEAT(ALT_PERIOD, true) SCHED_FEAT(BASE_SLICE, true) + +SCHED_FEAT(HZ_BW, false) --=20 2.31.1