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 B0280C28D13 for ; Mon, 22 Aug 2022 16:35:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237078AbiHVQfR (ORCPT ); Mon, 22 Aug 2022 12:35:17 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55142 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237072AbiHVQfP (ORCPT ); Mon, 22 Aug 2022 12:35:15 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 81DFB419B5; Mon, 22 Aug 2022 09:35:14 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 1A06D60F91; Mon, 22 Aug 2022 16:35:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A9A6C433C1; Mon, 22 Aug 2022 16:35:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661186113; bh=y+S14L9OvviihyJrTKTyBpSCtDnXo0ez48uTpsNV6nU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=lyem7v7qG2dX54DKpJXyPnPgJ7xyn/xVuXitSa+rlVhFDoX8HpWPNpwKremUVOFCl UT4s1aS4bknHE7pC7qCfA/NiBqutcvzeOzyyvjV0vXti4iH9rJ9JEoKM9gpKB8rlkT W+jdZSpZTu1P7zh8gTQb358aD3IGTdA4t4bz2hITbtPMzV4bAJjRX6oUDqTHgITcQn x2LwTh9vWSVxrL3cRTCdVM/2fx14h31VLKlFnmDQh78IFVddHQwK9SNEVE1jR3S7hV j7jZ9n/tOUsyJ6i71cApIo5m+HPVY7zexaGVZmmqPq4cYAAsKHdPMFiZXeyE6x3qfT DTafXmwAAGNDw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 01A895C03F3; Mon, 22 Aug 2022 09:35:13 -0700 (PDT) Date: Mon, 22 Aug 2022 09:35:12 -0700 From: "Paul E. McKenney" To: Zhen Lei Cc: Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 2/2] rcu: Simplify the code logic of rcu_init_nohz() Message-ID: <20220822163512.GG6159@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220817014253.1982-1-thunder.leizhen@huawei.com> <20220817014253.1982-3-thunder.leizhen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220817014253.1982-3-thunder.leizhen@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Aug 17, 2022 at 09:42:53AM +0800, Zhen Lei wrote: > When CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or CONFIG_NO_HZ_FULL=y, additional > CPUs need to be added to 'rcu_nocb_mask'. But 'rcu_nocb_mask' may be not > available now, due to 'rcu_nocbs' is not specified. Check and initialize > 'rcu_nocb_mask' before using it. This code simplification strictly follows > this logic, compared with old implementations, unnecessary crossovers are > avoided and easy to understand. > > Signed-off-by: Zhen Lei This looks like a nice simplification, but I will wait for your response on Patch 1/1 before trying it out. Thanx, Paul > --- > kernel/rcu/tree_nocb.h | 32 +++++++++----------------------- > 1 file changed, 9 insertions(+), 23 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index ff763e7dc53551f..3c59b12f4465af1 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -1209,44 +1209,30 @@ EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload); > void __init rcu_init_nohz(void) > { > int cpu; > - bool need_rcu_nocb_mask = false; > - bool offload_all = false; > struct rcu_data *rdp; > + const struct cpumask *cpumask = NULL; > > #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) > - if (!cpumask_available(rcu_nocb_mask)) { > - need_rcu_nocb_mask = true; > - offload_all = true; > - } > -#endif /* #if defined(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) */ > - > -#if defined(CONFIG_NO_HZ_FULL) > - if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) { > - need_rcu_nocb_mask = true; > - offload_all = false; /* NO_HZ_FULL has its own mask. */ > - } > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ > + cpumask = cpu_possible_mask; > +#elif defined(CONFIG_NO_HZ_FULL) > + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) > + cpumask = tick_nohz_full_mask; > +#endif > > - if (need_rcu_nocb_mask) { > + if (cpumask) { > if (!cpumask_available(rcu_nocb_mask)) { > if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { > pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); > return; > } > } > + > + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask); > } > > if (!cpumask_available(rcu_nocb_mask)) > return; > > -#if defined(CONFIG_NO_HZ_FULL) > - if (tick_nohz_full_running) > - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); > -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ > - > - if (offload_all) > - cpumask_setall(rcu_nocb_mask); > - > if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { > pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); > cpumask_and(rcu_nocb_mask, cpu_possible_mask, > -- > 2.25.1 >