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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 76E15C28D13 for ; Tue, 23 Aug 2022 01:56:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239434AbiHWB4g (ORCPT ); Mon, 22 Aug 2022 21:56:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238889AbiHWB4e (ORCPT ); Mon, 22 Aug 2022 21:56:34 -0400 Received: from mail-pg1-x52a.google.com (mail-pg1-x52a.google.com [IPv6:2607:f8b0:4864:20::52a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A7BA15A8AE; Mon, 22 Aug 2022 18:56:33 -0700 (PDT) Received: by mail-pg1-x52a.google.com with SMTP id v4so10991556pgi.10; Mon, 22 Aug 2022 18:56:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc; bh=52uLVVw4OD/MmnAgXUgrzEyWZqqpz4jQXVq1BITqiTU=; b=J5SQdoMUfy8QU0dk3BdI3XN/7CWq638jbVqtMJmfc8Rv/swC03KFQGhCJPYl01e/fy lZR1ndXFZilVMiE8IJQN6qSNc4kMborGgVUXhe1v3s4eYdsYQP3wE/c9RdbYELQWp3y3 8C/wTdHjZpedwxprIFeEfBuZhYTY/nyBNOc+v2LAb2SSyayeTAN/jjhigPT1iY9rKDYb PbwV3YZrxzAUxYfKdddGnqhIUQPlfNeZk4B7hAxPNnGEbUYrnVhhiDPF6Fjdvqrc49ta wZsyVqrVSt2KW7ecmuSTlp5u1A7PePrqTHgk2Kax75rsk9t3jUOchp0iZ/htqYUxhvHa stow== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=52uLVVw4OD/MmnAgXUgrzEyWZqqpz4jQXVq1BITqiTU=; b=VNvx2t66vrQcHiV9mjgbg2oX8wMAf077khau9jn0N1upTDP+9EnzDMOzIyAEQY/jAp QvWYk543zUlmkiRa3ECreWLI61V8f9+5NuxMriHgPh5ocTX1mCQK4A4q7feA+zMdGeu2 qc07DjWNHe8giEq/omm+YXeTtwukg0SkNsHML+KmArO8QuXsD4POqX23NC+AZ9pmV8zP ZGS6+Z9HaYhkA6fgyq+zD68rQFIcFsjWvPbvuMKFLRx3RDFFIRTZT7lrB3wGH6J/g2mD BWsEdrqk+lOTVqHPSBc0x7c6RLEYxxz42X5vG+5D2q1c58KipsF04uBNiweqiMQJg669 boFw== X-Gm-Message-State: ACgBeo2PxSbtVXCou9eTWkzDtKu5vv3Y3ZcGTAcnZCgFxHrw1T39uxUA WUT77BfOWEYi9CBM6iq7gw== X-Google-Smtp-Source: AA6agR7h7xSl/z3TGVwSD54jfHeZ1CgXBYOv2hr/Tr1j+C3lpBiHRt+LHdC1q+/p4ujI+KkcOYXNpA== X-Received: by 2002:a65:57c1:0:b0:42a:aaf6:c3b3 with SMTP id q1-20020a6557c1000000b0042aaaf6c3b3mr6722639pgr.26.1661219793120; Mon, 22 Aug 2022 18:56:33 -0700 (PDT) Received: from piliu.users.ipa.redhat.com ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id p11-20020a170902780b00b001714fa07b74sm2100918pll.108.2022.08.22.18.56.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Aug 2022 18:56:32 -0700 (PDT) Date: Tue, 23 Aug 2022 09:56:24 +0800 From: Pingfan Liu To: Joel Fernandes Cc: LKML , rcu , "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Thomas Gleixner , Steven Price , Mark Rutland , Kuppuswamy Sathyanarayanan , "Jason A. Donenfeld" Subject: Re: [RFC 06/10] rcu/hotplug: Make rcutree_dead_cpu() parallel Message-ID: References: <20220822021520.6996-1-kernelfans@gmail.com> <20220822021520.6996-7-kernelfans@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 22, 2022 at 02:08:38PM -0400, Joel Fernandes wrote: > On Sun, Aug 21, 2022 at 10:16 PM Pingfan Liu wrote: > > > > In order to support parallel, rcu_state.n_online_cpus should be > > atomic_dec() > > What does Parallel mean? Is that some kexec terminology? > 'Parallel' means concurrent. It is not a kexec terminology, instead, should be SMP. Thanks, Pingfan > Thanks, > > - Joel > > > > > Signed-off-by: Pingfan Liu > > Cc: "Paul E. McKenney" > > Cc: Frederic Weisbecker > > Cc: Neeraj Upadhyay > > Cc: Josh Triplett > > Cc: Steven Rostedt > > Cc: Mathieu Desnoyers > > Cc: Lai Jiangshan > > Cc: Joel Fernandes > > Cc: Thomas Gleixner > > Cc: Steven Price > > Cc: "Peter Zijlstra > > Cc: Mark Rutland > > Cc: Kuppuswamy Sathyanarayanan > > Cc: "Jason A. Donenfeld" > > To: linux-kernel@vger.kernel.org > > To: rcu@vger.kernel.org > > --- > > kernel/cpu.c | 1 + > > kernel/rcu/tree.c | 3 ++- > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/cpu.c b/kernel/cpu.c > > index 1261c3f3be51..90debbe28e85 100644 > > --- a/kernel/cpu.c > > +++ b/kernel/cpu.c > > @@ -1872,6 +1872,7 @@ static struct cpuhp_step cpuhp_hp_states[] = { > > .name = "RCU/tree:prepare", > > .startup.single = rcutree_prepare_cpu, > > .teardown.single = rcutree_dead_cpu, > > + .support_kexec_parallel = true, > > }, > > /* > > * On the tear-down path, timers_dead_cpu() must be invoked > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > > index 79aea7df4345..07d31e16c65e 100644 > > --- a/kernel/rcu/tree.c > > +++ b/kernel/rcu/tree.c > > @@ -2168,7 +2168,8 @@ int rcutree_dead_cpu(unsigned int cpu) > > if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) > > return 0; > > > > - WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); > > + /* Hot remove path allows parallel, while Hot add races against remove on lock */ > > + atomic_dec((atomic_t *)&rcu_state.n_online_cpus); > > /* Adjust any no-longer-needed kthreads. */ > > rcu_boost_kthread_setaffinity(rnp, -1); > > // Stop-machine done, so allow nohz_full to disable tick. > > -- > > 2.31.1 > >