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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 EEB31C433F5 for ; Thu, 16 Sep 2021 14:28:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D2A2261241 for ; Thu, 16 Sep 2021 14:28:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238178AbhIPO3S (ORCPT ); Thu, 16 Sep 2021 10:29:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48062 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236200AbhIPO3O (ORCPT ); Thu, 16 Sep 2021 10:29:14 -0400 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9A123C061574; Thu, 16 Sep 2021 07:27:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=e0kfV41WHc7RPbsfEn/+AVY29neHekRcD2dCKV7QMcM=; b=BiF8x1PthcevAOjk6Qz7pofGsD w407n0EDr4M1O2zwSRUvxdJPtOL8loYME+Sk/Gfi+cibd8CgcdfOSMQyY5t7FNz/4+cqtK2DQofV9 45+AoJT5XCZXqp772e225znV1A8ZymeOQ7D3lBfhWzBMfP7z5z0RjC448dnX+u4DNLLDEZZGprfuj u696plFmD3TMEqpuhc1VJ+L+zF/tgCecZ/zCupul6NR1hWe/tzC06pnVITv1pgFafzm4nL7zquQTf GEjAraOApAHlNd0DiJ5SmTcEtb8xowPaoXPulb3/eL5MQtdTyYRPAHw44SKuXpTIidLBhQn1l3MHn oloD1Eiw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1mQsMB-003fkK-5I; Thu, 16 Sep 2021 14:27:19 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id E41C530003A; Thu, 16 Sep 2021 16:27:15 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B46E62CEC0F72; Thu, 16 Sep 2021 16:27:15 +0200 (CEST) Date: Thu, 16 Sep 2021 16:27:15 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, 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, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Juri Lelli Subject: Re: [PATCH rcu 11/14] rcu: Make rcu_normal_after_boot writable again Message-ID: References: <20210915233305.GA3906641@paulmck-ThinkPad-P17-Gen-1> <20210915233343.3906738-11-paulmck@kernel.org> <20210916135712.GB4156@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210916135712.GB4156@paulmck-ThinkPad-P17-Gen-1> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 16, 2021 at 06:57:12AM -0700, Paul E. McKenney wrote: > RT systems they avoid expedited grace periods by booting with either > the rcupdate.rcu_normal or the rcupdate.rcu_normal_after_boot kernel > boot parameters. And here is the definition for the latter: > > static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT); > > In other words, RT systems shut off expedited grace periods by default, > and are thus free to use nohz_full CPU or not, as they choose. When using > nohz_full, they can also enable expedited grace periods by booting with > rcupdate.rcu_normal_after_boot=0. Or not, sysadm's choice. > > So I am not seeing a problem here. What am I missing? That wasn't at all clear to me from the Changelog. I thought it was enabling expedited crud for RT.