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 7AAC7ECAA25 for ; Thu, 25 Aug 2022 17:27:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242355AbiHYR1B (ORCPT ); Thu, 25 Aug 2022 13:27:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35462 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235860AbiHYR06 (ORCPT ); Thu, 25 Aug 2022 13:26:58 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1321F52E62; Thu, 25 Aug 2022 10:26:57 -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 C9D4FB82834; Thu, 25 Aug 2022 17:26:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7A439C433C1; Thu, 25 Aug 2022 17:26:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1661448414; bh=/rcIdqtB2P6iUhnIL5JW7YYpPCPj/25ZRKFDG/RtITM=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=rT2jSHeufFJU/maQgO5YBF9vvIFx0Rcje/woqO0WSNwNCU0wSAKGBNSifWRQ4qRPZ fbhl1QhsAUbbXmTDy9cAfo5OfobOuzzTXBdVNw1vrZfdgezx1serrUbIF352CR7oyz I+1E8nO83DXF079HbAR83y6d7ymEdyzl2COFfGBrJ7KqpG5K2oZnjPMtrfFHfxfFxh 5ZlQjmjAuEJF9ufADwxpQNTP49OqqgA/2BkSLKEI7oEP6YvKkqrsuNeHilt4Gd646o XWnZN43WeyJTts2NHwS1WtpkQlquJFlYpqQapcgFeTLpcd40WipAi4BQb4bX1xMK98 NwD+vwhTyyFMQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 15B025C055A; Thu, 25 Aug 2022 10:26:54 -0700 (PDT) Date: Thu, 25 Aug 2022 10:26:54 -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 v5 1/1] rcu: Simplify the code logic of rcu_init_nohz() Message-ID: <20220825172654.GP6159@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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220825092311.179-2-thunder.leizhen@huawei.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? 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 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,