From nobody Sun Feb 8 13:39:34 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 B8C19C0015E for ; Wed, 9 Aug 2023 19:35:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232444AbjHITfA (ORCPT ); Wed, 9 Aug 2023 15:35:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56884 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229549AbjHITe7 (ORCPT ); Wed, 9 Aug 2023 15:34:59 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 911F0C6; Wed, 9 Aug 2023 12:34:58 -0700 (PDT) Date: Wed, 09 Aug 2023 19:34:56 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1691609697; h=from:from:sender:sender:reply-to: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: in-reply-to:in-reply-to:references:references; bh=avhK83ETWP+EY52vf4zLFeVecnpAb5UyL56sNJqk+tY=; b=Z6bdaSlIVL4+kIU5D0u3PWYlBYwO5u8fxgVBop70bqezX44gZ7Pe8UEZXUdeIQGi64pY8C 6EnHEQ4fcOZqkV42zMtqSdpyDZX2dIWhILTUIg8b7fqf5+WcXcESdQ2iYjglTRonoP4wE5 rWUBstjMgntBUGGkR/acK4kPSOIq9uCBn16ESkDD/z4xQIHoS/nI35giivwCNNAndFcC0b Aee7QxbwWgzVk5pY3x4ERUXyP+X8kGrCBxIZ6fSlndLs1djc3mguTlDGxLcoxkOIRzk8NB MjAbzwuVMkF1XfG0tBfhd7QN61QKIGRhKD0wSdZmS/zSihvytzyIhfyJuj6wqA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1691609697; h=from:from:sender:sender:reply-to: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: in-reply-to:in-reply-to:references:references; bh=avhK83ETWP+EY52vf4zLFeVecnpAb5UyL56sNJqk+tY=; b=Il+nCp4+NtR6dOvEggwyxPP6e6HYPFGGbnNa6RmjKl7zO0fRxPCMra1jKAuyUHHNNT/qWI 49nSanUZ+8fcmzBQ== From: "tip-bot2 for Phil Auld" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched/fair: Block nohz tick_stop when cfs bandwidth in use Cc: Phil Auld , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230712133357.381137-3-pauld@redhat.com> References: <20230712133357.381137-3-pauld@redhat.com> MIME-Version: 1.0 Message-ID: <169160969649.27769.9219750044644784611.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 88c56cfeaec4642aee8aac58b38d5708c6aae0d3 Gitweb: https://git.kernel.org/tip/88c56cfeaec4642aee8aac58b38d5708c= 6aae0d3 Author: Phil Auld AuthorDate: Wed, 12 Jul 2023 09:33:57 -04:00 Committer: Peter Zijlstra CommitterDate: Wed, 02 Aug 2023 16:19:26 +02:00 sched/fair: Block nohz tick_stop when cfs bandwidth in use 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. Currently, 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. We use cfs_b->hierarchical_quota to determine if the task requires the tick. Add check in pick_next_task_fair() as well since that is where we have a handle on the task that is actually going to be running. Add check in sched_can_stop_tick() to cover some edge cases such as nr_running going from 2->1 and the 1 remains the running task. Reviewed-By: Ben Segall Signed-off-by: Phil Auld Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20230712133357.381137-3-pauld@redhat.com --- kernel/sched/core.c | 26 ++++++++++++++++++++- kernel/sched/fair.c | 52 +++++++++++++++++++++++++++++++++++++++- kernel/sched/features.h | 2 ++- kernel/sched/sched.h | 2 ++- 4 files changed, 81 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 3af25ca..614271a 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1194,6 +1194,20 @@ static void nohz_csd_func(void *info) #endif /* CONFIG_NO_HZ_COMMON */ =20 #ifdef CONFIG_NO_HZ_FULL +static inline bool __need_bw_check(struct rq *rq, struct task_struct *p) +{ + if (rq->nr_running !=3D 1) + return false; + + if (p->sched_class !=3D &fair_sched_class) + return false; + + if (!task_on_rq_queued(p)) + return false; + + return true; +} + bool sched_can_stop_tick(struct rq *rq) { int fifo_nr_running; @@ -1229,6 +1243,18 @@ bool sched_can_stop_tick(struct rq *rq) if (rq->nr_running > 1) return false; =20 + /* + * If there is one task and it has CFS runtime bandwidth constraints + * and it's on the cpu now we don't want to stop the tick. + * This check prevents clearing the bit if a newly enqueued task here is + * dequeued by migrating while the constrained task continues to run. + * E.g. going from 2->1 without going through pick_next_task(). + */ + if (sched_feat(HZ_BW) && __need_bw_check(rq, rq->curr)) { + if (cfs_task_bw_constrained(rq->curr)) + return false; + } + return true; } #endif /* CONFIG_NO_HZ_FULL */ diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 26bfbb6..c282064 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6189,6 +6189,46 @@ static void __maybe_unused unthrottle_offline_cfs_rq= s(struct rq *rq) rq_clock_stop_loop_update(rq); } =20 +bool cfs_task_bw_constrained(struct task_struct *p) +{ + struct cfs_rq *cfs_rq =3D task_cfs_rq(p); + + if (!cfs_bandwidth_used()) + return false; + + if (cfs_rq->runtime_enabled || + tg_cfs_bandwidth(cfs_rq->tg)->hierarchical_quota !=3D RUNTIME_INF) + return true; + + return false; +} + +#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) +{ + 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) + 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_task_bw_constrained(p)) + tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED); +} +#endif + #else /* CONFIG_CFS_BANDWIDTH */ =20 static inline bool cfs_bandwidth_used(void) @@ -6231,9 +6271,18 @@ 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) {} - +#ifdef CONFIG_CGROUP_SCHED +bool cfs_task_bw_constrained(struct task_struct *p) +{ + return false; +} +#endif #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: */ @@ -8201,6 +8250,7 @@ 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 ee7f23c..e10074c 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, true) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 602de71..19af176 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -459,6 +459,7 @@ extern void init_cfs_bandwidth(struct cfs_bandwidth *cf= s_b, struct cfs_bandwidth extern void __refill_cfs_bandwidth_runtime(struct cfs_bandwidth *cfs_b); extern void start_cfs_bandwidth(struct cfs_bandwidth *cfs_b); extern void unthrottle_cfs_rq(struct cfs_rq *cfs_rq); +extern bool cfs_task_bw_constrained(struct task_struct *p); =20 extern void init_tg_rt_entry(struct task_group *tg, struct rt_rq *rt_rq, struct sched_rt_entity *rt_se, int cpu, @@ -494,6 +495,7 @@ static inline void set_task_rq_fair(struct sched_entity= *se, #else /* CONFIG_CGROUP_SCHED */ =20 struct cfs_bandwidth { }; +static inline bool cfs_task_bw_constrained(struct task_struct *p) { return= false; } =20 #endif /* CONFIG_CGROUP_SCHED */