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 16BEFECAAD4 for ; Fri, 26 Aug 2022 13:47:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S243574AbiHZNr1 (ORCPT ); Fri, 26 Aug 2022 09:47:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45208 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344378AbiHZNpZ (ORCPT ); Fri, 26 Aug 2022 09:45:25 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D1B5943E73; Fri, 26 Aug 2022 06:45:23 -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 ams.source.kernel.org (Postfix) with ESMTPS id D7FE6B82F84; Fri, 26 Aug 2022 13:45:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8466CC433D6; Fri, 26 Aug 2022 13:45:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661521520; bh=/wCO+8NSsd2IYaROtKGfH5tdFKHXG6nMlG+xYwW1HJk=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=oZUROb8qX+9vmEmC4yo3jFzm26WdhONdNte9Nj1h7bIjlxeM0fdO/WkSUsg2SmV5I FGlDnvy9isRLKMkqtfXr6i6Oh8WMQzZSttVt2iIaHtC9/Z4jsHYGl9+O9/METg+xFH PsL8XHqVghg+eFaG4Tn8YTHEdDIT7wOBHtTEou6eM8vP6aOX/TqQN9DLLkCXVRTMaY 7EnAsvKAyq6PqBURbknt42CUz9ZuWEQ+PlCXayS5d7UUBZa3YJSX2BlofCs+JqWPyb DUsbjGkYUwFVWA9c7ql/21r+TBd8gSrjmkzo66Nnxc+guBh2RSTZbzaDyKrKu+fCdB 94IqVvvTF2dvw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 1FF0F5C03F3; Fri, 26 Aug 2022 06:45:20 -0700 (PDT) Date: Fri, 26 Aug 2022 06:45:20 -0700 From: "Paul E. McKenney" To: "Leizhen (ThunderTown)" 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 v5 1/1] rcu: Simplify the code logic of rcu_init_nohz() Message-ID: <20220826134520.GS6159@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220825092311.179-1-thunder.leizhen@huawei.com> <20220825092311.179-2-thunder.leizhen@huawei.com> <20220825172654.GP6159@paulmck-ThinkPad-P17-Gen-1> <43370a3c-8c7a-c7c7-ac2b-bec2bf6c8728@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <43370a3c-8c7a-c7c7-ac2b-bec2bf6c8728@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 26, 2022 at 09:42:11AM +0800, Leizhen (ThunderTown) wrote: > > > On 2022/8/26 1:26, Paul E. McKenney wrote: > > On Thu, Aug 25, 2022 at 05:23:11PM +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 > > > > Much nicer, thank you! > > > > As usual, I could not resist the urge to wordsmith. Could you please > > check to make sure that I did not mess anything up? > > Okay, thank you very much. The boot option name "rcu_nocb_mask=" is > incorrect, should be "rcu_nocbs=". Good eyes, thank you! I will fix this on the next rebase. Thanx, Paul > > ------------------------------------------------------------------------ > > > > commit 4ac3b3d1a19943b1522c0b1d0895aefbb80ec294 > > Author: Zhen Lei > > Date: Thu Aug 25 17:23:11 2022 +0800 > > > > rcu: Simplify rcu_init_nohz() cpumask handling > > > > In kernels built with either CONFIG_RCU_NOCB_CPU_DEFAULT_ALL=y or > > CONFIG_NO_HZ_FULL=y, additional CPUs must be added to rcu_nocb_mask. > > Except that kernels booted without the rcu_nocb_mask= will not have > > rcu_nocb_mask= ----> rcu_nocbs= > > > allocated rcu_nocb_mask. And the current rcu_init_nohz() function uses > > its need_rcu_nocb_mask and offload_all local variables to track the > > rcu_nocb and nohz_full state. > > > > But there is a much simpler approach, namely creating a cpumask pointer > > to track the default and then using cpumask_available() to check the > > rcu_nocb_mask state. This commit takes this approach, thereby simplifying > > and shortening the rcu_init_nohz() function. > > > > Signed-off-by: Zhen Lei > > Signed-off-by: Paul E. McKenney > > > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > > index 0a5f0ef414845..c8167be2288fa 100644 > > --- a/kernel/rcu/tree_nocb.h > > +++ b/kernel/rcu/tree_nocb.h > > @@ -1210,45 +1210,31 @@ 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 (!rcu_state.nocb_is_setup) { > > - 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); > > rcu_state.nocb_is_setup = true; > > } > > > > if (!rcu_state.nocb_is_setup) > > 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, > > . > > > > -- > Regards, > Zhen Lei