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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 B50B8C433ED for ; Mon, 19 Apr 2021 16:51:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 93AE961166 for ; Mon, 19 Apr 2021 16:51:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239300AbhDSQwQ (ORCPT ); Mon, 19 Apr 2021 12:52:16 -0400 Received: from shelob.surriel.com ([96.67.55.147]:32784 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231674AbhDSQwL (ORCPT ); Mon, 19 Apr 2021 12:52:11 -0400 Received: from [2603:3005:d05:2b00:6e0b:84ff:fee2:98bb] (helo=imladris.surriel.com) by shelob.surriel.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94) (envelope-from ) id 1lYX7X-00053n-AQ; Mon, 19 Apr 2021 12:51:35 -0400 Date: Mon, 19 Apr 2021 12:51:34 -0400 From: Rik van Riel To: linux-kernel@vger.kernel.org Cc: Kernel Team , Peter Zijlstra , Ingo Molnar , Dietmar Eggemann , Mel Gorman , Valentin Schneider , Vincent Guittot Subject: [PATCH v2] sched,fair: skip newidle_balance if a wakeup is pending Message-ID: <20210419125134.5cab12ea@imladris.surriel.com> X-Mailer: Claws Mail 3.17.6 (GTK+ 2.24.32; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: riel@shelob.surriel.com Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The try_to_wake_up function has an optimization where it can queue a task for wakeup on its previous CPU, if the task is still in the middle of going to sleep inside schedule(). Once schedule() re-enables IRQs, the task will be woken up with an IPI, and placed back on the runqueue. If we have such a wakeup pending, there is no need to search other CPUs for runnable tasks. Just skip (or bail out early from) newidle balancing, and run the just woken up task. For a memcache like workload test, this reduces total CPU use by about 2%, proportionally split between user and system time, and p99 and p95 application response time by 2-3% on average. The schedstats run_delay number shows a similar improvement. Signed-off-by: Rik van Riel --- v2: - fix !SMP build error and prev-not-CFS case by moving check into newidle_balance - fix formatting of if condition - audit newidle_balance return value use to make sure we get that right - reset idle_stamp when breaking out of the loop due to ->ttwu_pending kernel/sched/fair.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 69680158963f..5e26f013e182 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10594,6 +10594,14 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) u64 curr_cost = 0; update_misfit_status(NULL, this_rq); + + /* + * There is a task waiting to run. No need to search for one. + * Return 0; the task will be enqueued when switching to idle. + */ + if (this_rq->ttwu_pending) + return 0; + /* * We must set idle_stamp _before_ calling idle_balance(), such that we * measure the duration of idle_balance() as idle time. @@ -10661,7 +10669,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) * Stop searching for tasks to pull if there are * now runnable tasks on this rq. */ - if (pulled_task || this_rq->nr_running > 0) + if (pulled_task || this_rq->nr_running > 0 || + this_rq->ttwu_pending) break; } rcu_read_unlock(); @@ -10688,7 +10697,7 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) if (this_rq->nr_running != this_rq->cfs.h_nr_running) pulled_task = -1; - if (pulled_task) + if (pulled_task || this_rq->ttwu_pending) this_rq->idle_stamp = 0; rq_repin_lock(this_rq, rf); -- 2.25.4