From nobody Mon Apr 13 18:46:22 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 DA564C43217 for ; Tue, 15 Nov 2022 17:19:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231460AbiKORTU (ORCPT ); Tue, 15 Nov 2022 12:19:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231755AbiKORTD (ORCPT ); Tue, 15 Nov 2022 12:19:03 -0500 Received: from mail-wr1-x434.google.com (mail-wr1-x434.google.com [IPv6:2a00:1450:4864:20::434]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CE9B813D3C for ; Tue, 15 Nov 2022 09:19:01 -0800 (PST) Received: by mail-wr1-x434.google.com with SMTP id o4so25327485wrq.6 for ; Tue, 15 Nov 2022 09:19:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=references:in-reply-to:message-id:date:subject:cc:to:from:from:to :cc:subject:date:message-id:reply-to; bh=0gt5dMxvQbqno+STaQibPwy3l5gz8MECmjhw94KguxM=; b=gDlAKnk9+Ms0Le2gLFVmU+3clOP59GSKkv9GngIkekxRvYns5OBHP80f5OAv2vvvM6 J+9Sirc0kDuo0uRHvG85cjSAkntieDPfLiP5zLdnqEGiekLQi1Y9xp9ysNHXp6BN2j8u csCvr+rbhPeDVHLK0q3y2kcJ7DmQdTCEV+YxeGbAL8bDAN3FPq+Q3YXlCKuY7cghq40q OUerFuSRsmo4hMCll1BI73vbcS8mXd8gtz3SXsD8y0kJI47XE5RKYuU0ecUK2TMzKDx6 VgTYxklpL3Zaz+uTu+bh0+Oq6SSTXVcS7J8s5+y/rp9fH4WYeZpt4m7o+8YdyuZb3EhV Yl+A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=references:in-reply-to:message-id:date:subject:cc:to:from :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=0gt5dMxvQbqno+STaQibPwy3l5gz8MECmjhw94KguxM=; b=lICA+aSGDZHSfjSj5UBRWdQTMJNoW4n5/kEdJtXlFYpwVzf32jWMOoOVgPWilA0N/I GrbPWYjzSz4M0pkWUpRKRe0ghK6lVJ7L8MVVYPz8loSniXezxCbIRxQxQxJTHjAGyyen DV37kqmENPQfTxkKR10mvxr/VVBOaQNpGzVN58eqeoyJRL5y79m7l5brX4BJ0zktSpGs Ge2csK9bHW9N4Q9W3h00kUKnPWbtw4OwwHNbXpgJ/9cqTFVYcpBrTTPzUF5hNYADmed8 ZEJKuVnV0Rwqx7cGmcJYfoeQlEEqTcKbiMSyvY25FxTvyJTMWtvRDNsr9v1TQTKpQds9 BtKg== X-Gm-Message-State: ANoB5pnx1OqBjCScoH2gxvuJ6q/3rbb+5RXbnNZ7DT3kyNXItmAQqBvA 3URnEu6yO8avxhXUfwM3SFQKCw== X-Google-Smtp-Source: AA0mqf55iZ1zHnxQ5HbFIfLc/TFTuq0dFnRpy4KDRhkgi1eznszPpqvaI5E1NktaD9oG9R+8+/nvAw== X-Received: by 2002:adf:e702:0:b0:236:695b:6275 with SMTP id c2-20020adfe702000000b00236695b6275mr11843770wrm.116.1668532739919; Tue, 15 Nov 2022 09:18:59 -0800 (PST) Received: from localhost.localdomain ([2a01:e0a:f:6020:91c8:7496:8b73:811f]) by smtp.gmail.com with ESMTPSA id bg40-20020a05600c3ca800b003cf78aafdd7sm16846461wmb.39.2022.11.15.09.18.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Nov 2022 09:18:59 -0800 (PST) From: Vincent Guittot To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, linux-kernel@vger.kernel.org, parth@linux.ibm.com Cc: qyousef@layalina.io, chris.hyser@oracle.com, patrick.bellasi@matbug.net, David.Laight@aculab.com, pjt@google.com, pavel@ucw.cz, tj@kernel.org, qperret@google.com, tim.c.chen@linux.intel.com, joshdon@google.com, timj@gnu.org, kprateek.nayak@amd.com, yu.c.chen@intel.com, youssefesmat@chromium.org, joel@joelfernandes.org, Vincent Guittot Subject: [PATCH v9 1/9] sched/fair: fix unfairness at wakeup Date: Tue, 15 Nov 2022 18:18:43 +0100 Message-Id: <20221115171851.835-2-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20221115171851.835-1-vincent.guittot@linaro.org> References: <20221115171851.835-1-vincent.guittot@linaro.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" At wake up, the vruntime of a task is updated to not be more older than a sched_latency period behind the min_vruntime. This prevents long sleeping task to get unlimited credit at wakeup. Such waking task should preempt current one to use its CPU bandwidth but wakeup_gran() can be larger than sched_latency, filter out the wakeup preemption and as a results steals some CPU bandwidth to the waking task. Make sure that a task, which vruntime has been capped, will preempt current task and use its CPU bandwidth even if wakeup_gran() is in the same range as sched_latency. If the waking task failed to preempt current it could to wait up to sysctl_sched_min_granularity before preempting it during next tick. Strictly speaking, we should use cfs->min_vruntime instead of curr->vruntime but it doesn't worth the additional overhead and complexity as the vruntime of current should be close to min_vruntime if not equal. Reported-by: Youssef Esmat Signed-off-by: Vincent Guittot --- kernel/sched/fair.c | 46 ++++++++++++++++++++------------------------ kernel/sched/sched.h | 34 +++++++++++++++++++++++++++++++- 2 files changed, 54 insertions(+), 26 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4cc56c91e06e..c8a697f8db88 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4645,33 +4645,17 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_en= tity *se, int initial) { u64 vruntime =3D cfs_rq->min_vruntime; =20 - /* - * The 'current' period is already promised to the current tasks, - * however the extra weight of the new task will slow them down a - * little, place the new task so that it fits in the slot that - * stays open at the end. - */ - if (initial && sched_feat(START_DEBIT)) - vruntime +=3D sched_vslice(cfs_rq, se); - - /* sleeps up to a single latency don't count. */ - if (!initial) { - unsigned long thresh; - - if (se_is_idle(se)) - thresh =3D sysctl_sched_min_granularity; - else - thresh =3D sysctl_sched_latency; - + if (!initial) + /* sleeps up to a single latency don't count. */ + vruntime -=3D get_sleep_latency(se_is_idle(se)); + else if (sched_feat(START_DEBIT)) /* - * Halve their sleep time's effect, to allow - * for a gentler effect of sleepers: + * The 'current' period is already promised to the current tasks, + * however the extra weight of the new task will slow them down a + * little, place the new task so that it fits in the slot that + * stays open at the end. */ - if (sched_feat(GENTLE_FAIR_SLEEPERS)) - thresh >>=3D 1; - - vruntime -=3D thresh; - } + vruntime +=3D sched_vslice(cfs_rq, se); =20 /* ensure we never gain time by being placed backwards. */ se->vruntime =3D max_vruntime(se->vruntime, vruntime); @@ -7520,6 +7504,18 @@ wakeup_preempt_entity(struct sched_entity *curr, str= uct sched_entity *se) return -1; =20 gran =3D wakeup_gran(se); + + /* + * At wake up, the vruntime of a task is capped to not be older than + * a sched_latency period compared to min_vruntime. This prevents long + * sleeping task to get unlimited credit at wakeup. Such waking up task + * has to preempt current in order to not lose its share of CPU + * bandwidth but wakeup_gran() can become higher than scheduling period + * for low priority task. Make sure that long sleeping task will get a + * chance to preempt current. + */ + gran =3D min_t(s64, gran, get_latency_max()); + if (vdiff > gran) return 1; =20 diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 771f8ddb7053..842ce0094d9c 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2453,9 +2453,9 @@ extern void check_preempt_curr(struct rq *rq, struct = task_struct *p, int flags); extern const_debug unsigned int sysctl_sched_nr_migrate; extern const_debug unsigned int sysctl_sched_migration_cost; =20 -#ifdef CONFIG_SCHED_DEBUG extern unsigned int sysctl_sched_latency; extern unsigned int sysctl_sched_min_granularity; +#ifdef CONFIG_SCHED_DEBUG extern unsigned int sysctl_sched_idle_min_granularity; extern unsigned int sysctl_sched_wakeup_granularity; extern int sysctl_resched_latency_warn_ms; @@ -2470,6 +2470,38 @@ extern unsigned int sysctl_numa_balancing_scan_size; extern unsigned int sysctl_numa_balancing_hot_threshold; #endif =20 +static inline unsigned long get_sleep_latency(bool idle) +{ + unsigned long thresh; + + if (idle) + thresh =3D sysctl_sched_min_granularity; + else + thresh =3D sysctl_sched_latency; + + /* + * Halve their sleep time's effect, to allow + * for a gentler effect of sleepers: + */ + if (sched_feat(GENTLE_FAIR_SLEEPERS)) + thresh >>=3D 1; + + return thresh; +} + +static inline unsigned long get_latency_max(void) +{ + unsigned long thresh =3D get_sleep_latency(false); + + /* + * If the waking task failed to preempt current it could to wait up to + * sysctl_sched_min_granularity before preempting it during next tick. + */ + thresh -=3D sysctl_sched_min_granularity; + + return thresh; +} + #ifdef CONFIG_SCHED_HRTICK =20 /* --=20 2.17.1