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=-13.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 1D8D5C433E2 for ; Mon, 31 Aug 2020 18:11:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E9F7F2083E for ; Mon, 31 Aug 2020 18:11:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598897492; bh=oNI0rVyhAa3e3M0tZqUyhGaWitcL9S6WNg3KZaOXpts=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oyvo1M4nW8/9aZbU+70kIFXVX6hgMQy3A7+dl0CDDSLksolC1TapHH8JpguQpwMWZ ZTkkZU0butalzldCvjVU8/GeasBOTx8+8H094uspQZBlSDZ67TeYDwrHJij5wPzZ4c VcSjEeD1vgAwRurrqD4VgQjNuBt5Pf6OA1Jym1rg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729370AbgHaSLb (ORCPT ); Mon, 31 Aug 2020 14:11:31 -0400 Received: from mail.kernel.org ([198.145.29.99]:35812 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728885AbgHaSLW (ORCPT ); Mon, 31 Aug 2020 14:11:22 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6859A21473; Mon, 31 Aug 2020 18:11:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598897482; bh=oNI0rVyhAa3e3M0tZqUyhGaWitcL9S6WNg3KZaOXpts=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=xlPYFOgAhxbA2tlWpScktn/PuyVp1TuYbusp0YeZIqMqVpXrm2B7tybWOIOPZjl5L mKhE9wl9SF6+evZDd2MPhQWQasM6obWUpnWnla45gBY2Am2tvdJNWNbHIHgH3T/yjR sA4TLKqV3MVzlELUKyq4JruziFAzLKYhD8+62Z/0= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 03/13] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs Date: Mon, 31 Aug 2020 11:11:10 -0700 Message-Id: <20200831181120.1044-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200831181101.GA950@paulmck-ThinkPad-P72> References: <20200831181101.GA950@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" If there are idle CPUs, RCU's grace-period kthread will wait several jiffies before even thinking about polling them. This promotes efficiency, which is normally a good thing, but when the kernel has been built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, we care more about short grace periods. This commit therefore restricts the default jiffies_till_first_fqs value to zero in kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y, which causes RCU's grace-period kthread to poll for idle CPUs immediately after starting a grace period. Reported-by Jann Horn Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8ce77d9..8551159 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -485,7 +485,7 @@ module_param(qhimark, long, 0444); module_param(qlowmark, long, 0444); module_param(qovld, long, 0444); -static ulong jiffies_till_first_fqs = ULONG_MAX; +static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX; static ulong jiffies_till_next_fqs = ULONG_MAX; static bool rcu_kick_kthreads; static int rcu_divisor = 7; -- 2.9.5