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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6634C433FE for ; Thu, 2 Dec 2021 00:29:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354335AbhLBAcs (ORCPT ); Wed, 1 Dec 2021 19:32:48 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43902 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354301AbhLBAcm (ORCPT ); Wed, 1 Dec 2021 19:32:42 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 31265C061757; Wed, 1 Dec 2021 16:29:20 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id CC945B821A2; Thu, 2 Dec 2021 00:29:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0424BC58328; Thu, 2 Dec 2021 00:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638404955; bh=0R8xOedkXzTnCsDGtaj4inEzmhi04D3LV4RmfZyGtHk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=AVUjK6lKkFALEZDwacDBRr4YfLWjzgDkgiGjjX/cY8hAUOmOqaSbnFyrY94vuMaMo h7n/vsYgeUpVP1PI4xQUi7aj5xnsVqGkE5TrkPhvvULDJSaO6lI1jNUhM/dNWsGhyD iNvk44YNT7TgwE94QclCFAVEM7DB3alGcm/04KFtpPNQQnznRXSJBtmX9dEPY9HZ4j OkRRb6B6uFzK/JR8DCuHjyAw2sW2owyxFB69oIcWKUWMbkz80hEJ/6bDn3yHyBrZvu hshUIlgdU0Ox5cp8ZYgOdtTLaDjUVP5J17t9Xjt5WTuUOmk3K3x+KCVZTC6pWTtkA4 dVqOjAuJ+tkUQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 708915C13F6; Wed, 1 Dec 2021 16:29:14 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Frederic Weisbecker , Valentin Schneider , Sebastian Andrzej Siewior , Boqun Feng , Neeraj Upadhyay , Uladzislau Rezki , "Paul E . McKenney" Subject: [PATCH rcu 10/18] rcu: Fix callbacks processing time limit retaining cond_resched() Date: Wed, 1 Dec 2021 16:29:04 -0800 Message-Id: <20211202002912.3127710-10-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> References: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Frederic Weisbecker The callbacks processing time limit makes sure we are not exceeding a given amount of time executing the queue. However its "continue" clause bypasses the cond_resched() call on rcuc and NOCB kthreads, delaying it until we reach the limit, which can be very long... Make sure the scheduler has a higher priority than the time limit. Reviewed-by: Valentin Schneider Tested-by: Valentin Schneider Tested-by: Sebastian Andrzej Siewior Signed-off-by: Frederic Weisbecker Cc: Valentin Schneider Cc: Peter Zijlstra Cc: Sebastian Andrzej Siewior Cc: Josh Triplett Cc: Joel Fernandes Cc: Boqun Feng Cc: Neeraj Upadhyay Cc: Uladzislau Rezki Cc: Thomas Gleixner Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 4f4d9ea6a9cb5..74e210ccfd382 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2525,9 +2525,21 @@ static void rcu_do_batch(struct rcu_data *rdp) /* * Stop only if limit reached and CPU has something to do. */ - if (count >= bl && in_serving_softirq() && - (need_resched() || !is_idle_task(current))) - break; + if (in_serving_softirq()) { + if (count >= bl && (need_resched() || !is_idle_task(current))) + break; + } else { + local_bh_enable(); + lockdep_assert_irqs_enabled(); + cond_resched_tasks_rcu_qs(); + lockdep_assert_irqs_enabled(); + local_bh_disable(); + } + + /* + * Make sure we don't spend too much time here and deprive other + * softirq vectors of CPU cycles. + */ if (unlikely(tlimit)) { /* only call local_clock() every 32 callbacks */ if (likely((count & 31) || local_clock() < tlimit)) @@ -2535,13 +2547,6 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Exceeded the time limit, so leave. */ break; } - if (!in_serving_softirq()) { - local_bh_enable(); - lockdep_assert_irqs_enabled(); - cond_resched_tasks_rcu_qs(); - lockdep_assert_irqs_enabled(); - local_bh_disable(); - } } rcu_nocb_lock_irqsave(rdp, flags); -- 2.31.1.189.g2e36527f23