From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D12E6C3A59E for ; Thu, 22 Aug 2019 02:19:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AB30022DD3 for ; Thu, 22 Aug 2019 02:19:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730886AbfHVCSw (ORCPT ); Wed, 21 Aug 2019 22:18:52 -0400 Received: from shelob.surriel.com ([96.67.55.147]:34142 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730876AbfHVCSN (ORCPT ); Wed, 21 Aug 2019 22:18:13 -0400 Received: from imladris.surriel.com ([96.67.55.152]) by shelob.surriel.com with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.92) (envelope-from ) id 1i0cfX-0001S6-6N; Wed, 21 Aug 2019 22:17:43 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: kernel-team@fb.com, pjt@google.com, dietmar.eggemann@arm.com, peterz@infradead.org, mingo@redhat.com, morten.rasmussen@arm.com, tglx@linutronix.de, mgorman@techsingularity.net, vincent.guittot@linaro.org, Rik van Riel Subject: [PATCH 05/15] sched,fair: remove cfs_rqs from leaf_cfs_rq_list bottom up Date: Wed, 21 Aug 2019 22:17:30 -0400 Message-Id: <20190822021740.15554-6-riel@surriel.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190822021740.15554-1-riel@surriel.com> References: <20190822021740.15554-1-riel@surriel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Reducing the overhead of the CPU controller is achieved by not walking all the sched_entities every time a task is enqueued or dequeued. One of the things being checked every single time is whether the cfs_rq is on the rq->leaf_cfs_rq_list. By only removing a cfs_rq from the list once it no longer has children on the list, we can avoid walking the sched_entity hierarchy if the bottom cfs_rq is on the list, once the runqueues have been flattened. Signed-off-by: Rik van Riel Suggested-by: Vincent Guittot --- kernel/sched/fair.c | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index a48d0dbfc232..04b216234265 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -369,6 +369,39 @@ static inline void assert_list_leaf_cfs_rq(struct rq *rq) SCHED_WARN_ON(rq->tmp_alone_branch != &rq->leaf_cfs_rq_list); } +/* + * Because list_add_leaf_cfs_rq always places a child cfs_rq on the list + * immediately before a parent cfs_rq, and cfs_rqs are removed from the list + * bottom-up, we only have to test whether the cfs_rq before us on the list + * is our child. + */ +static inline bool child_cfs_rq_on_list(struct cfs_rq *cfs_rq) +{ + struct cfs_rq *prev_cfs_rq; + struct list_head *prev; + + prev = cfs_rq->leaf_cfs_rq_list.prev; + prev_cfs_rq = container_of(prev, struct cfs_rq, leaf_cfs_rq_list); + + return (prev_cfs_rq->tg->parent == cfs_rq->tg); +} + +/* + * Remove a cfs_rq from the list if it has no children on the list. + * The scheduler iterates over the list regularly; if conditions for + * removal are still true, we'll get to this cfs_rq in the future. + */ +static inline void list_del_leaf_cfs_rq_bottom(struct cfs_rq *cfs_rq) +{ + if (!cfs_rq->on_list) + return; + + if (child_cfs_rq_on_list(cfs_rq)) + return; + + list_del_leaf_cfs_rq(cfs_rq); +} + /* Iterate thr' all leaf cfs_rq's on a runqueue */ #define for_each_leaf_cfs_rq_safe(rq, cfs_rq, pos) \ list_for_each_entry_safe(cfs_rq, pos, &rq->leaf_cfs_rq_list, \ @@ -7723,7 +7756,7 @@ static void update_blocked_averages(int cpu) * decayed cfs_rqs linger on the list. */ if (cfs_rq_is_decayed(cfs_rq)) - list_del_leaf_cfs_rq(cfs_rq); + list_del_leaf_cfs_rq_bottom(cfs_rq); /* Don't need periodic decay once load/util_avg are null */ if (cfs_rq_has_blocked(cfs_rq)) -- 2.20.1