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=-20.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS 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 C3276C433ED for ; Thu, 22 Apr 2021 07:36:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7AA646145C for ; Thu, 22 Apr 2021 07:36:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235059AbhDVHgi (ORCPT ); Thu, 22 Apr 2021 03:36:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57692 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230316AbhDVHgh (ORCPT ); Thu, 22 Apr 2021 03:36:37 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C2F0BC06174A; Thu, 22 Apr 2021 00:36:02 -0700 (PDT) Date: Thu, 22 Apr 2021 07:36:00 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1619076961; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ygaHawp8T/kH373vVmhcmax1kMu0V4pX0+2ZN2xTwBM=; b=0QoGKYrpZGYtQRY/8RfcgQu65VvETTXQcHaAmWzLNXMsDDz1mnTYEha7P6JHur9C781uTI AWKREpCOtgozpw/SROB2NG0oOrvKtSSzwdv8GIYk+Vizf2uOnYwQbas96OCyD6HMoliGPV xzQvDuUTTH1z3nTNES3lqzxceXq3cpW63Fyrmgzm8lLfNEdXKKwlSjZvXCwMxjKGUlbRrL cyZdu3RyVxmzJbpJCjU9Q6Uv2Rds2q2k7D2LQc5lPzSwwCQjJTyMAzW/ume+Pm7FMyP09f MeThcewXpRaCxqi9Fr/ZDP1Q1C7F5DV1WcKFrVyogio5XfTztWxs/uDPk805cw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1619076961; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ygaHawp8T/kH373vVmhcmax1kMu0V4pX0+2ZN2xTwBM=; b=1a84TXPcwE0uJqUvxk35nVxxx2zZ3najR9b0DQzM3uBlfZsbQT+IHpG2/IV7MrWUq0yHuz 2bRaZMUEImawcOAA== From: "tip-bot2 for Rik van Riel" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] sched,fair: skip newidle_balance if a wakeup is pending Cc: Rik van Riel , "Peter Zijlstra (Intel)" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20210420120705.5c705d4b@imladris.surriel.com> References: <20210420120705.5c705d4b@imladris.surriel.com> MIME-Version: 1.0 Message-ID: <161907696062.29796.108437696048031441.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: 9c9f520a14670ad59da2f700660f7601ec9e0b07 Gitweb: https://git.kernel.org/tip/9c9f520a14670ad59da2f700660f7601ec9e0b07 Author: Rik van Riel AuthorDate: Tue, 20 Apr 2021 12:07:05 -04:00 Committer: Peter Zijlstra CommitterDate: Wed, 21 Apr 2021 13:55:43 +02:00 sched,fair: skip newidle_balance if a wakeup is pending 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 10% on average. The schedstats run_delay number shows a similar improvement. Signed-off-by: Rik van Riel Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20210420120705.5c705d4b@imladris.surriel.com --- kernel/sched/fair.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1d75af1..83cd2bd 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10592,6 +10592,14 @@ 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. @@ -10657,7 +10665,8 @@ 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(); @@ -10684,7 +10693,12 @@ out: if (time_after(this_rq->next_balance, next_balance)) this_rq->next_balance = next_balance; - if (pulled_task) + /* + * If we are no longer idle, do not let the time spent here pull + * down this_rq->avg_idle. That could lead to newidle_balance not + * doing enough work, and the CPU actually going idle. + */ + if (pulled_task || this_rq->ttwu_pending) this_rq->idle_stamp = 0; else nohz_newidle_balance(this_rq);