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 38CAAC32772 for ; Tue, 23 Aug 2022 14:50:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242425AbiHWOuy (ORCPT ); Tue, 23 Aug 2022 10:50:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49880 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242167AbiHWOuc (ORCPT ); Tue, 23 Aug 2022 10:50:32 -0400 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0372A2F1F7A; Tue, 23 Aug 2022 05:13:56 -0700 (PDT) Received: from dggpemm500023.china.huawei.com (unknown [172.30.72.53]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4MBp1n0b3jz1N7M7; Tue, 23 Aug 2022 20:09:33 +0800 (CST) Received: from dggpemm500006.china.huawei.com (7.185.36.236) by dggpemm500023.china.huawei.com (7.185.36.83) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 23 Aug 2022 20:13:01 +0800 Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Tue, 23 Aug 2022 20:13:01 +0800 Subject: Re: [PATCH v4 2/2] rcu: Simplify the code logic of rcu_init_nohz() To: CC: Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , "Steven Rostedt" , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , , References: <20220817014253.1982-1-thunder.leizhen@huawei.com> <20220817014253.1982-3-thunder.leizhen@huawei.com> <20220822163512.GG6159@paulmck-ThinkPad-P17-Gen-1> From: "Leizhen (ThunderTown)" Message-ID: Date: Tue, 23 Aug 2022 20:13:00 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20220822163512.GG6159@paulmck-ThinkPad-P17-Gen-1> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/8/23 0:35, Paul E. McKenney wrote: > 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. How about I post v5 and just do this simplification? Patch 1/2 seems to require further discussion and in-depth analysis, which may take a long time. > > 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 >> > . > -- Regards, Zhen Lei