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 19A3DC00140 for ; Wed, 24 Aug 2022 13:38:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238331AbiHXNi2 (ORCPT ); Wed, 24 Aug 2022 09:38:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54122 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238375AbiHXNiW (ORCPT ); Wed, 24 Aug 2022 09:38:22 -0400 Received: from mail-lf1-x136.google.com (mail-lf1-x136.google.com [IPv6:2a00:1450:4864:20::136]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A4D347D7BB; Wed, 24 Aug 2022 06:38:21 -0700 (PDT) Received: by mail-lf1-x136.google.com with SMTP id n15so2960079lfe.3; Wed, 24 Aug 2022 06:38:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc; bh=OdBnoS8zGnfacBUoB38O3wipMG6DwRHyyQgDcbST94Y=; b=BCzSMmHT4nrXEhbH+xrvIhbKLDFCz8BfUSaUvbExriat86XTcUJqUXmZozIcLok1+U Nm8y5nFXpVX1Weeizbj+m6+foV4ZUpCNN/aSrbmDzssnL0KyUgdNqqpsskqXth91KhEU VG51XEejAMiszJ8tnoG2PmJjz8sibLv+urZYVMlxULaDk5M+qOVPuxXW5FJFmPxDtq5B PLRIBxjadn8ld+q9izfiVagHkOrY6a39nuWfQLqHzZYlKHxfFDE+enjrnfnr8jivK1NB VVtdldxUstBr+TJFEWPCjLiYAzlNIuv/othu/hrCunbCR3Wlr+GN82eVOagu130Z/F81 MfRw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc; bh=OdBnoS8zGnfacBUoB38O3wipMG6DwRHyyQgDcbST94Y=; b=rhe1R8SXCySx0zvMEkMciZ2eLhOka/utCR6dBh4AF0FkToT6nujpb4HISxRKJp4jkE dxYl8HmMSNKxNylTpiW4LdaoJnQpbUpP5S98Gu/IgWjpSa8QtbvJJ5ws+I89L7v9VbB8 ocncbJsBKantdANN2hxGUY25JZHrM2LZP+33O7jZcFJsAs/dG6Ln4inU4sz82demo3En KfVfIpWi6ANbwfA5XilgI7C8kbTQ4TzHJ09ZIyeGAnDzz5oSenPx9KKdxLidXAykRBoI +pI9h+Fl3+E7ztpzrqprxmhJt2x39waVyJR4v+7yY6LI7vpJx/2BMo0jKxFL+vfGOUsd Zhzw== X-Gm-Message-State: ACgBeo11XWEHKhRl7SpjXMi+uMiWNqUd2ka32JHcWd4pua92aP+1w4lr H2nX+aLTN/4rYHDJRBQMPfJOHgFufG9dyCHNDA== X-Google-Smtp-Source: AA6agR7Z0zmPZ2oTAyl5ghHIdjlSL5e3Ijh1+AfwqpZX6nNCu1Q6vqfZNvjO8c9qRfVSO0gGPMo+SZIWqcvHyA1ZcWw= X-Received: by 2002:a05:6512:228a:b0:48a:fa84:e298 with SMTP id f10-20020a056512228a00b0048afa84e298mr9475953lfu.183.1661348299946; Wed, 24 Aug 2022 06:38:19 -0700 (PDT) MIME-Version: 1.0 References: <20220822021520.6996-1-kernelfans@gmail.com> <20220822021520.6996-7-kernelfans@gmail.com> In-Reply-To: From: Pingfan Liu Date: Wed, 24 Aug 2022 21:38:08 +0800 Message-ID: Subject: Re: [RFC 06/10] rcu/hotplug: Make rcutree_dead_cpu() parallel 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" Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Aug 23, 2022 at 11:14 AM Joel Fernandes wrote: > > On Mon, Aug 22, 2022 at 9:56 PM Pingfan Liu wrote: > > > > 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. > > Ah ok! Makes sense. Apologies to be the word-police here, but you > probably could reword it to "In order to support parallel offlining" > or some such. > Thanks for your advice. It is a good English lesson, which can give more productivity in the community. Thanks, Pingfan > - Joel > > > > > > > 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 > > > >