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[2620:137:e000::1:20]) by mx.google.com with ESMTP id h24-20020a63c018000000b004639c772888si18630488pgg.225.2022.11.10.09.50.54; Thu, 10 Nov 2022 09:51:07 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=uqF7wYco; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231356AbiKJRuZ (ORCPT + 99 others); Thu, 10 Nov 2022 12:50:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231270AbiKJRuT (ORCPT ); Thu, 10 Nov 2022 12:50:19 -0500 Received: from mail-wr1-x42a.google.com (mail-wr1-x42a.google.com [IPv6:2a00:1450:4864:20::42a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9C2D83C6E4 for ; Thu, 10 Nov 2022 09:50:18 -0800 (PST) Received: by mail-wr1-x42a.google.com with SMTP id j15so3386552wrq.3 for ; Thu, 10 Nov 2022 09:50:18 -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=FulDXK+MjqUjf+jM0x0PxczJh4rRajiCQKKkLNt7L9g=; b=uqF7wYcoS1Vb/LeU+zmM+bWQUS+qz9nsrF2qaBasvtiFv8WBliA8otbDoW4M5B9cwq WyYJBfZgarq006JA96KlmAOBsILI2m/yIIl9TH5XlQZlQhqbt6L0C48uOa/lQwUqlb0e dUEkyyfWPCWzb+C/qL/jJNhesEP81sWPU+S8IemO62dyKhLOadbQ0Yr2ot3jnaHMpT4w HHv8T5aKurGZqFSIB3DDJJ26EOYDze3hRakZOMfuwqBmxYDsyNZ/qwWF//7Iw3R5Vifz ScMvIIPk2DaRqHmlyUGZPSx/MYUMdWgrq368eMR1B9K7LSAzkpWfxKENO404JPYFVvPJ 8uRQ== 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=FulDXK+MjqUjf+jM0x0PxczJh4rRajiCQKKkLNt7L9g=; b=Vct2NnNgKo7IMqunMAQ8X5FxXGZ3mD+GfUeQ31rvdsllvTjVB6tHUZqSSi4FSG9TRK ZF3JhQFkKkYHkiYXYqQwxyd+iXK5Q2hNBtaLmkRoPYANUNQFz5aI+wSnilQepzzxosfM ywAFTD9RYv4+Fed54bQcsJTC6SqeX4Py+QMxZrBaTmk00kotY9bheSvmZa/CK9oBqc4H mBU7OXUdoK1ET16C1P7oF00Bv9jK7WITC1iVzhiriKxgOeIGK8Zust+uduq79fd+oujA ZJNGdLisbU0aq1nE8+J0lFO9S4v6deT2D2VASw6JvIfRzPfaArQBFxvY44gBOndgxewB 77mA== X-Gm-Message-State: ACrzQf1RyCenywJyHYnGYWiIerlTH/KEqzjYDR33zD80yvhWLY1Gr4aM e/w0TY7kbz2d7AKzMqdeq077CA== X-Received: by 2002:adf:e104:0:b0:236:dce2:35dc with SMTP id t4-20020adfe104000000b00236dce235dcmr35917753wrz.675.1668102617044; Thu, 10 Nov 2022 09:50:17 -0800 (PST) Received: from localhost.localdomain ([2a01:e0a:f:6020:342a:468f:562a:9cc4]) by smtp.gmail.com with ESMTPSA id f6-20020a05600c4e8600b003cfc02ab8basm6514677wmq.33.2022.11.10.09.50.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Nov 2022 09:50:15 -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 v8 1/9] sched/fair: fix unfairness at wakeup Date: Thu, 10 Nov 2022 18:50:01 +0100 Message-Id: <20221110175009.18458-2-vincent.guittot@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20221110175009.18458-1-vincent.guittot@linaro.org> References: <20221110175009.18458-1-vincent.guittot@linaro.org> X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DIET_1,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1749132422442660334?= X-GMAIL-MSGID: =?utf-8?q?1749132422442660334?= 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. Signed-off-by: Vincent Guittot Reported-by: Youssef Esmat Reviewed-by: Joel Fernandes (Google) --- kernel/sched/fair.c | 46 ++++++++++++++++++++------------------------ kernel/sched/sched.h | 30 ++++++++++++++++++++++++++++- 2 files changed, 50 insertions(+), 26 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 5ffec4370602..eb04c83112a0 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4345,33 +4345,17 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) { u64 vruntime = cfs_rq->min_vruntime; - /* - * 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 += 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 = sysctl_sched_min_granularity; - else - thresh = sysctl_sched_latency; - + if (!initial) + /* sleeps up to a single latency don't count. */ + vruntime -= get_sched_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 >>= 1; - - vruntime -= thresh; - } + vruntime += sched_vslice(cfs_rq, se); /* ensure we never gain time by being placed backwards. */ se->vruntime = max_vruntime(se->vruntime, vruntime); @@ -7187,6 +7171,18 @@ wakeup_preempt_entity(struct sched_entity *curr, struct sched_entity *se) return -1; gran = 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 = min_t(s64, gran, get_latency_max()); + if (vdiff > gran) return 1; diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 1fc198be1ffd..14879d429919 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2432,9 +2432,9 @@ 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; -#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; @@ -2448,6 +2448,34 @@ extern unsigned int sysctl_numa_balancing_scan_period_max; extern unsigned int sysctl_numa_balancing_scan_size; #endif +static inline unsigned long get_sched_latency(bool idle) +{ + unsigned long thresh; + + if (idle) + thresh = sysctl_sched_min_granularity; + else + thresh = sysctl_sched_latency; + + /* + * Halve their sleep time's effect, to allow + * for a gentler effect of sleepers: + */ + if (sched_feat(GENTLE_FAIR_SLEEPERS)) + thresh >>= 1; + + return thresh; +} + +static inline unsigned long get_latency_max(void) +{ + unsigned long thresh = get_sched_latency(false); + + thresh -= sysctl_sched_min_granularity; + + return thresh; +} + #ifdef CONFIG_SCHED_HRTICK /*