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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 03260C433EF for ; Mon, 11 Oct 2021 14:52:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D99F760E98 for ; Mon, 11 Oct 2021 14:52:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243985AbhJKOyb (ORCPT ); Mon, 11 Oct 2021 10:54:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:33638 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237811AbhJKOy0 (ORCPT ); Mon, 11 Oct 2021 10:54:26 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 97A7260BD3; Mon, 11 Oct 2021 14:52:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1633963946; bh=iaUZfJFRip9ouAlmnyaHzyPKLPOsL/VzwlUShGOmbKQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iynkktKsGUIlDk0V3L+Yj1mf4smNOSy0tEmbJnnloNnzRxl0wBmRmktWi/lNXfvzA RJ7gEtmDHGcq4j5caC9vIGYMkZNzh56NyuDz6aFPXOwwFglJ6RQfGPIdr/8bYMwjL3 JdzLZSkS9zuha0qQ+nHHEQwkBsjpFfuRt+wadmh33C4obMqM3mo7V76cVoNsWZtUV2 Y2gfmv3inOsd9J+pEFy1XUy9WjaSwin9IVKbSqC7t1b9tKB+F2O7tWu0EAbd7WKJ7N KK15/e91vBM3qKsFFv7p3y4bP3cnVk5B5OUb2b2osg7vMofdpbDnNkmIkLaLXxeBCW 9gucXDgqdHDZQ== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Sebastian Andrzej Siewior , Valentin Schneider , Peter Zijlstra , Uladzislau Rezki , Thomas Gleixner , Valentin Schneider , Boqun Feng , Neeraj Upadhyay , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH 09/11] rcu: Fix callbacks processing time limit retaining cond_resched() Date: Mon, 11 Oct 2021 16:51:38 +0200 Message-Id: <20211011145140.359412-10-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211011145140.359412-1-frederic@kernel.org> References: <20211011145140.359412-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- 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 716dead1509d..7a655d93a28a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2535,9 +2535,21 @@ 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)) @@ -2545,13 +2557,6 @@ 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); -- 2.25.1