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=-19.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,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 8F53BC433B4 for ; Tue, 11 May 2021 22:53:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7468861934 for ; Tue, 11 May 2021 22:53:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230367AbhEKWyf (ORCPT ); Tue, 11 May 2021 18:54:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:33908 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230291AbhEKWyO (ORCPT ); Tue, 11 May 2021 18:54:14 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 113246193F; Tue, 11 May 2021 22:53:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620773587; bh=0zvL868RbLnDBhdNNXkDTbR3Z2jBxOtL487by24P1Ss=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=hGAiEIBnDv/W8n1d+nPT+INxssGlEzVGruW4451VoohL7UqcRWFsOm0OI0zva8ENP EhA2tbGayte8uMJXQqjn1NZY/CGfRHrVZmrwKzrY7a4KgjVMN8bbOGauMt/sxQU7im 5QDcHdmrDiQCgxYMDlBneIKnPuxDt8mOfCtvnKDWnSpZZ6hgRLQ3kKk3c/DD3eipwZ 8JjZxGHov1LH/SMWylfOwQt0ckUoRehE4LByTJIQeCD+6Gb/jvyIrEIiP5p5WJieX6 SKgHZyBtBt+grIdBNF4gGFsZN1ztPad57wIQAj3vtrR3kWKJMJBLTlOH+r9pDFM3GA bcG6sLbmrUVtA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 9CC835C0DF5; Tue, 11 May 2021 15:53:06 -0700 (PDT) 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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 12/19] rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs Date: Tue, 11 May 2021 15:52:57 -0700 Message-Id: <20210511225304.2893154-12-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20210511225241.GA2893003@paulmck-ThinkPad-P17-Gen-1> References: <20210511225241.GA2893003@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Kernels built with CONFIG_RCU_STRICT_GRACE_PERIOD=y can experience significant lock contention due to RCU's resulting focus on ending grace periods as soon as possible. This is OK, but only if there are not very many CPUs. This commit therefore puts this Kconfig option off-limits to systems with more than four CPUs. Signed-off-by: Paul E. McKenney --- kernel/rcu/Kconfig.debug | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug index 1942c1f1bb65..4fd64999300f 100644 --- a/kernel/rcu/Kconfig.debug +++ b/kernel/rcu/Kconfig.debug @@ -116,7 +116,7 @@ config RCU_EQS_DEBUG config RCU_STRICT_GRACE_PERIOD bool "Provide debug RCU implementation with short grace periods" - depends on DEBUG_KERNEL && RCU_EXPERT + depends on DEBUG_KERNEL && RCU_EXPERT && NR_CPUS <= 4 default n select PREEMPT_COUNT if PREEMPT=n help -- 2.31.1.189.g2e36527f23