From nobody Thu Apr 30 08:28:12 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 B0A37C433EF for ; Wed, 1 Jun 2022 02:19:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349097AbiFACTH (ORCPT ); Tue, 31 May 2022 22:19:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35178 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231168AbiFACTF (ORCPT ); Tue, 31 May 2022 22:19:05 -0400 Received: from mail-pl1-x629.google.com (mail-pl1-x629.google.com [IPv6:2607:f8b0:4864:20::629]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B643866F88 for ; Tue, 31 May 2022 19:19:03 -0700 (PDT) Received: by mail-pl1-x629.google.com with SMTP id d22so431618plr.9 for ; Tue, 31 May 2022 19:19:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=jrSgvQyWeWdspWWG5kiYDhk1wMiZW92w4und9ira2PQ=; b=c9Y3Vw3cUEiGeX57Gj16eI1xRXLF5q9aZUIMPBbMUWEVDDaPLeBcYVhGAa7Eop5Yj+ yJqvWefb14fWT4STfn/eoo7HfCtXEBoxNfM8QdfvnEqAxdc4xFQgh3cYF1HG99E7rGUJ y9a7BD10MikzVUmJmdeaUnGNGDyW7MeoZnl4q+ax37NMv+3c+/PcAInf05+9QYypp6ur To7OUiEKyurXQi4hoMr/ZE3iy2LSdk19YucxHkBY/hNQL6EK8Ql2AjUAkVEpRKtkgR7O Xd6wH9OP5yksT+Rpa09d6KgKFtFgbw1PmxOd/iSoM7Z6v2z2QpuH7N0+ip5VEfCtWxGk Oqtw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=jrSgvQyWeWdspWWG5kiYDhk1wMiZW92w4und9ira2PQ=; b=C6iX72+PmILwS4J3egfV2GPkmFJqQWLeDlUU8P4971W2d+MB1jY7S6uZHeq0ILxXhO Aa1qExQF7Jsfg94ZHyJW3Cpm+qz2rtbWJZqI7u8qmOQgTyFjKLV9yyUMWjrE8D8xdWOg QGZ/RIyHWJrvIGImlCJxffzmtt7LZIejF+sSGioqFGsz/5HhvQcSsP/rbEuPfu81evBS /gWrqxwQ2v7/Gg79g//Kqc2sb3Q9Slw4tAo+c95HadIATyDhASV33t195M/vzqtnH8f4 j5OjiklcL51+D4s8Vjd407bfbeChxrbavg0/5IFRDlmluZiKFQlY5wVh/Pkeyw7r0WDO PY/A== X-Gm-Message-State: AOAM532vpHGeY8jEmDlnb8g6lW/OXsnNp3XAUlI54JE1cTvzHbC7bEOL XSrnmsNsxQgpViE5+pJFtYk6CQ== X-Google-Smtp-Source: ABdhPJyqXEmVU4IMnY1jfM1LMVL3J3vp8vuOeKHhRnNDr6bGOgoOMoPgq7lTX58hSF7Fb8Ker307AQ== X-Received: by 2002:a17:90b:46c6:b0:1e3:524c:7f94 with SMTP id jx6-20020a17090b46c600b001e3524c7f94mr3267751pjb.177.1654049943208; Tue, 31 May 2022 19:19:03 -0700 (PDT) Received: from C02CV1DAMD6P.bytedance.net ([139.177.225.231]) by smtp.gmail.com with ESMTPSA id f70-20020a623849000000b0050dc762817esm134462pfa.88.2022.05.31.19.18.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 31 May 2022 19:19:02 -0700 (PDT) From: Chengming Zhou To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com Cc: linux-kernel@vger.kernel.org, duanxiongchun@bytedance.com, songmuchun@bytedance.com, zhengqi.arch@bytedance.com, Chengming Zhou Subject: [PATCH v4] sched/fair: optimize and simplify rq leaf_cfs_rq_list Date: Wed, 1 Jun 2022 10:18:48 +0800 Message-Id: <20220601021848.76943-1-zhouchengming@bytedance.com> X-Mailer: git-send-email 2.35.1 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" We notice the rq leaf_cfs_rq_list has two problems when do bugfix backports and some test profiling. 1. cfs_rqs under throttled subtree could be added to the list, and make their fully decayed ancestors on the list, even though not needed. 2. #1 also make the leaf_cfs_rq_list management complex and error prone, this is the list of related bugfix so far: commit 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()") commit fe61468b2cbc ("sched/fair: Fix enqueue_task_fair warning") commit b34cb07dde7c ("sched/fair: Fix enqueue_task_fair() warning some m= ore") commit 39f23ce07b93 ("sched/fair: Fix unthrottle_cfs_rq() for leaf_cfs_r= q list") commit 0258bdfaff5b ("sched/fair: Fix unfairness caused by missing load = decay") commit a7b359fc6a37 ("sched/fair: Correctly insert cfs_rq's to list on u= nthrottle") commit fdaba61ef8a2 ("sched/fair: Ensure that the CFS parent is added af= ter unthrottling") commit 2630cde26711 ("sched/fair: Add ancestors of unthrottled undecayed= cfs_rq") commit 31bc6aeaab1d ("sched/fair: Optimize update_blocked_averages()") delete every cfs_rq under throttled subtree from rq->leaf_cfs_rq_list, and delete the throttled_hierarchy() test in update_blocked_averages(), which optimized update_blocked_averages(). But those later bugfix add cfs_rqs under throttled subtree back to rq->leaf_cfs_rq_list again, with their fully decayed ancestors, for the integrity of rq->leaf_cfs_rq_list. This patch takes another method, skip all cfs_rqs under throttled hierarchy when list_add_leaf_cfs_rq(), to completely make cfs_rqs under throttled subtree off the leaf_cfs_rq_list. So we don't need to consider throttled related things in enqueue_entity(), unthrottle_cfs_rq() and enqueue_task_fair(), which simplify the code a lot. Also optimize update_blocked_averages() since cfs_rqs under throttled hierarchy and their ancestors won't be on the leaf_cfs_rq_list. Signed-off-by: Chengming Zhou Reviewed-by: Vincent Guittot --- v4: - make sure the attach/detach is propagated down up to the throttled cfs_rq. Thanks Vincent. v3: - fix !CONFIG_FAIR_GROUP_SCHED build error, reported by kernel test robot v2: - move throttled_hierarchy() outside list_add_leaf_cfs_rq(), suggested by Vincent. --- kernel/sched/fair.c | 92 ++++++++++++++------------------------------- 1 file changed, 28 insertions(+), 64 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 77b2048a9326..b3371fa40548 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3144,6 +3144,8 @@ void reweight_task(struct task_struct *p, int prio) load->inv_weight =3D sched_prio_to_wmult[prio]; } =20 +static inline int throttled_hierarchy(struct cfs_rq *cfs_rq); + #ifdef CONFIG_FAIR_GROUP_SCHED #ifdef CONFIG_SMP /* @@ -3254,8 +3256,6 @@ static long calc_group_shares(struct cfs_rq *cfs_rq) } #endif /* CONFIG_SMP */ =20 -static inline int throttled_hierarchy(struct cfs_rq *cfs_rq); - /* * Recomputes the group entity based on the current state of its group * runqueue. @@ -4368,16 +4368,11 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_= entity *se, int flags) __enqueue_entity(cfs_rq, se); se->on_rq =3D 1; =20 - /* - * When bandwidth control is enabled, cfs might have been removed - * because of a parent been throttled but cfs->nr_running > 1. Try to - * add it unconditionally. - */ - if (cfs_rq->nr_running =3D=3D 1 || cfs_bandwidth_used()) - list_add_leaf_cfs_rq(cfs_rq); - - if (cfs_rq->nr_running =3D=3D 1) + if (cfs_rq->nr_running =3D=3D 1) { check_enqueue_throttle(cfs_rq); + if (!throttled_hierarchy(cfs_rq)) + list_add_leaf_cfs_rq(cfs_rq); + } } =20 static void __clear_buddies_last(struct sched_entity *se) @@ -4992,11 +4987,18 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) /* update hierarchical throttle state */ walk_tg_tree_from(cfs_rq->tg, tg_nop, tg_unthrottle_up, (void *)rq); =20 - /* Nothing to run but something to decay (on_list)? Complete the branch */ if (!cfs_rq->load.weight) { - if (cfs_rq->on_list) - goto unthrottle_throttle; - return; + if (!cfs_rq->on_list) + return; + /* + * Nothing to run but something to decay (on_list)? + * Complete the branch. + */ + for_each_sched_entity(se) { + if (list_add_leaf_cfs_rq(cfs_rq_of(se))) + break; + } + goto unthrottle_throttle; } =20 task_delta =3D cfs_rq->h_nr_running; @@ -5034,31 +5036,12 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq) /* end evaluation on encountering a throttled cfs_rq */ if (cfs_rq_throttled(qcfs_rq)) goto unthrottle_throttle; - - /* - * One parent has been throttled and cfs_rq removed from the - * list. Add it back to not break the leaf list. - */ - if (throttled_hierarchy(qcfs_rq)) - list_add_leaf_cfs_rq(qcfs_rq); } =20 /* At this point se is NULL and we are at root level*/ add_nr_running(rq, task_delta); =20 unthrottle_throttle: - /* - * The cfs_rq_throttled() breaks in the above iteration can result in - * incomplete leaf list maintenance, resulting in triggering the - * assertion below. - */ - for_each_sched_entity(se) { - struct cfs_rq *qcfs_rq =3D cfs_rq_of(se); - - if (list_add_leaf_cfs_rq(qcfs_rq)) - break; - } - assert_list_leaf_cfs_rq(rq); =20 /* Determine whether we need to wake up potentially idle CPU: */ @@ -5713,13 +5696,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct = *p, int flags) /* end evaluation on encountering a throttled cfs_rq */ if (cfs_rq_throttled(cfs_rq)) goto enqueue_throttle; - - /* - * One parent has been throttled and cfs_rq removed from the - * list. Add it back to not break the leaf list. - */ - if (throttled_hierarchy(cfs_rq)) - list_add_leaf_cfs_rq(cfs_rq); } =20 /* At this point se is NULL and we are at root level*/ @@ -5743,21 +5719,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct = *p, int flags) update_overutilized_status(rq); =20 enqueue_throttle: - if (cfs_bandwidth_used()) { - /* - * When bandwidth control is enabled; the cfs_rq_throttled() - * breaks in the above iteration can result in incomplete - * leaf list maintenance, resulting in triggering the assertion - * below. - */ - for_each_sched_entity(se) { - cfs_rq =3D cfs_rq_of(se); - - if (list_add_leaf_cfs_rq(cfs_rq)) - break; - } - } - assert_list_leaf_cfs_rq(rq); =20 hrtick_update(rq); @@ -11287,9 +11248,13 @@ static inline bool vruntime_normalized(struct task= _struct *p) */ static void propagate_entity_cfs_rq(struct sched_entity *se) { - struct cfs_rq *cfs_rq; + struct cfs_rq *cfs_rq =3D cfs_rq_of(se); + + if (cfs_rq_throttled(cfs_rq)) + return; =20 - list_add_leaf_cfs_rq(cfs_rq_of(se)); + if (!throttled_hierarchy(cfs_rq)) + list_add_leaf_cfs_rq(cfs_rq); =20 /* Start to propagate at parent */ se =3D se->parent; @@ -11297,14 +11262,13 @@ static void propagate_entity_cfs_rq(struct sched_= entity *se) for_each_sched_entity(se) { cfs_rq =3D cfs_rq_of(se); =20 - if (!cfs_rq_throttled(cfs_rq)){ - update_load_avg(cfs_rq, se, UPDATE_TG); - list_add_leaf_cfs_rq(cfs_rq); - continue; - } + update_load_avg(cfs_rq, se, UPDATE_TG); =20 - if (list_add_leaf_cfs_rq(cfs_rq)) + if (cfs_rq_throttled(cfs_rq)) break; + + if (!throttled_hierarchy(cfs_rq)) + list_add_leaf_cfs_rq(cfs_rq); } } #else --=20 2.36.1