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 02F6EC32774 for ; Mon, 22 Aug 2022 18:08:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236244AbiHVSIx (ORCPT ); Mon, 22 Aug 2022 14:08:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59958 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234980AbiHVSIv (ORCPT ); Mon, 22 Aug 2022 14:08:51 -0400 Received: from mail-io1-xd2f.google.com (mail-io1-xd2f.google.com [IPv6:2607:f8b0:4864:20::d2f]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E90D41D0DA for ; Mon, 22 Aug 2022 11:08:49 -0700 (PDT) Received: by mail-io1-xd2f.google.com with SMTP id h78so8971191iof.13 for ; Mon, 22 Aug 2022 11:08:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc; bh=WgzWzZj00zOWLrpbCwQ4WTwiDIwDcKzbwKa8iAf7tLg=; b=OWC1nKVBtluEW62ASQUxzNEKPaHq+xaPILPsqberXSM3ZYA8aUQyGYB7lYfxVvO3Kx 02oQPI4Hbh1a3fXkORCfP/LGkRxymrN2VbrNgvOeSz6RdEkVVWDFzSS/DH1ojr0uBAqu IGw2jTYyP8dKkaI73RXI091fqraCH6NvcfoR0= 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=WgzWzZj00zOWLrpbCwQ4WTwiDIwDcKzbwKa8iAf7tLg=; b=rIZbmXTV83zE3oAk2LDZuQiHeQov9+pzX+HFlIXp/xgqsBGMxJkgX3RzLO4u74E8/R 8SGRFkQGMZCSvo5GxmTkHo40op6plEpFTQYf3vzlxearB0RVFVXyEJqOe54zuJHeZntQ otMqI5UHO3+F03f89R0ehfG8baJauBCFIqQMrcGXfpF0VxWElmeY/JeXiQiKuGWuz9l6 MWwf0/oQgZ23SlrD3Gjp5n0mazm3lV3AFnXvj/ebci9LTk2bIPVzKdjRUOmQjCt938tN +LrqdkKNS2/0w8AxBy2t2rWD3y1NC45vsvPHzWhSazXZYw5l4mw7J4ygISncC4QKbXJu jo7g== X-Gm-Message-State: ACgBeo3G7h20yAtX6mnx22mYYKHv8ukWytBVTD1fOjQx9mGl+op3Y+za t61pqJGaJGcRZR+KQdUjB1glVUEoBw7qJTiqo/od/A== X-Google-Smtp-Source: AA6agR7cV0NmQ6+Pqp4g7/80o66iJ+BRcBW4jtTnfFVQmkwALzchwVQ5BWOGJnuehHgZpFba5YCOnN125O5Tw0wa6SA= X-Received: by 2002:a5d:9914:0:b0:67c:2039:caff with SMTP id x20-20020a5d9914000000b0067c2039caffmr9103230iol.201.1661191729339; Mon, 22 Aug 2022 11:08:49 -0700 (PDT) MIME-Version: 1.0 References: <20220822021520.6996-1-kernelfans@gmail.com> <20220822021520.6996-7-kernelfans@gmail.com> In-Reply-To: <20220822021520.6996-7-kernelfans@gmail.com> From: Joel Fernandes Date: Mon, 22 Aug 2022 14:08:38 -0400 Message-ID: Subject: Re: [RFC 06/10] rcu/hotplug: Make rcutree_dead_cpu() parallel To: Pingfan Liu 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 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? 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 >