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 287C5C433E0 for ; Wed, 12 Aug 2020 22:58:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F267A22BF5 for ; Wed, 12 Aug 2020 22:58:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597273093; bh=zy2r+61uBN1pJktsl9IlZc4fSFAY3znZwPcoLkq3Cks=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=RfzFwRGxDDcQ4f9GNIECIt6E1IDJ4N+7yJze8tCPPFUwuvGh05ZK9WoGTHf7NNfr5 78NGIPoRoNT1JsYoFyoSWKQBo0+NAoCcVRx5F0aheg7hZJ9fZk/e+Y/GT6u129DIa3 IcPXPRXBomqdCtvoxRTKk64v42XP2bu28skkumOs= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726604AbgHLW5f (ORCPT ); Wed, 12 Aug 2020 18:57:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:48906 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726510AbgHLW5f (ORCPT ); Wed, 12 Aug 2020 18:57:35 -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 D9CC620B1F; Wed, 12 Aug 2020 22:57:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597273055; bh=zy2r+61uBN1pJktsl9IlZc4fSFAY3znZwPcoLkq3Cks=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vxGaqD4DmxDokpJs2n5WPT9IROUgwWeJHCnNjedqnlRtj3b+uj2O622ohACXLb2Gj S5W8zyuysfCLCA/bitzzDv3fIHDUrIPV/8WCbgPRChou2apmlxbe3FsXWd181euH1h hGVp85bIted2Ei+MPnJndWvanlyb7kLRbbmDepGI= 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, elver@google.com, dvyukov@google.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 03/12] rcu: Restrict default jiffies_till_first_fqs for strict RCU GPs Date: Wed, 12 Aug 2020 15:57:23 -0700 Message-Id: <20200812225732.20068-3-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200812225632.GA19759@paulmck-ThinkPad-P72> References: <20200812225632.GA19759@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@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 65e1b5e..d333f1b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -471,7 +471,7 @@ 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