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 93EF0C433EF for ; Thu, 2 Dec 2021 00:29:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1354443AbhLBAc4 (ORCPT ); Wed, 1 Dec 2021 19:32:56 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43910 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354320AbhLBAcm (ORCPT ); Wed, 1 Dec 2021 19:32:42 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 442A2C061759; Wed, 1 Dec 2021 16:29:20 -0800 (PST) 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 sin.source.kernel.org (Postfix) with ESMTPS id 83DF8CE2146; Thu, 2 Dec 2021 00:29:18 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F9F6C58339; Thu, 2 Dec 2021 00:29:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638404955; bh=ZjKmJJlETmOFDExkKIrDiHC63737vzU73zR5NOaeV7k=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bXiZ/dVOhBhQvRsIaA8Wn9eSjAiXeknMcB24IoDS8GyPzTJYPHzJgzm53hPZ7kRlZ PQDSstHkMxfk6WaScb7XzHnnztXV2ICcXQ50l3Fr4vLhiNG6r/tvHmHpnVrk4SY4Jo XmMQwoesR7CXYuMx5K2L2eTIB6C/MfeofmyJrR8vPSjkIx/Kf12FXnjLnJMafE81W3 2jcMvPVstyQs1mXqC+q8vtgtRxspyq8TZByL5sGyepKTXd91dXQ0KErRkjNEW6rHUB g0igQbDgFL0A8Sx+9oO8mkz+fHt0ff4j9+tli736feE+A+SUKVcqJNvHKufwfFQkrx GWyv4f/0r/qeA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 7A97D5C1495; Wed, 1 Dec 2021 16:29:14 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, Frederic Weisbecker , Neeraj Upadhyay , Boqun Feng , Uladzislau Rezki , Juri Lelli , "Paul E . McKenney" Subject: [PATCH rcu 15/18] rcu/nocb: Optimize kthreads and rdp initialization Date: Wed, 1 Dec 2021 16:29:09 -0800 Message-Id: <20211202002912.3127710-15-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> References: <20211202002848.GA3127439@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: Frederic Weisbecker Currently cpumask_available() is used to prevent from unwanted NOCB initialization. However if neither "rcu_nocbs=" nor "nohz_full=" parameters are passed to a kernel built with CONFIG_CPUMASK_OFFSTACK=n, the initialization path is still taken, running through all sorts of needless operations and iterations on an empty cpumask. Fix this by relying on a real initialization state instead. This also optimizes kthread creation, preventing needless iteration over all online CPUs when the kernel is booted without any offloaded CPUs. Signed-off-by: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes Tested-by: Juri Lelli Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_nocb.h | 24 +++++++++++++++++------- 1 file changed, 17 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index cd596cf4ee79a..42092de677054 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -60,6 +60,9 @@ static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. * If the list is invalid, a warning is emitted and all CPUs are offloaded. */ + +static bool rcu_nocb_is_setup; + static int __init rcu_nocb_setup(char *str) { alloc_bootmem_cpumask_var(&rcu_nocb_mask); @@ -67,6 +70,7 @@ static int __init rcu_nocb_setup(char *str) pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); cpumask_setall(rcu_nocb_mask); } + rcu_nocb_is_setup = true; return 1; } __setup("rcu_nocbs=", rcu_nocb_setup); @@ -1167,13 +1171,17 @@ void __init rcu_init_nohz(void) need_rcu_nocb_mask = true; #endif /* #if defined(CONFIG_NO_HZ_FULL) */ - if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) { - if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { - pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); - return; + if (need_rcu_nocb_mask) { + 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; + } } + rcu_nocb_is_setup = true; } - if (!cpumask_available(rcu_nocb_mask)) + + if (!rcu_nocb_is_setup) return; #if defined(CONFIG_NO_HZ_FULL) @@ -1275,8 +1283,10 @@ static void __init rcu_spawn_nocb_kthreads(void) { int cpu; - for_each_online_cpu(cpu) - rcu_spawn_cpu_nocb_kthread(cpu); + if (rcu_nocb_is_setup) { + for_each_online_cpu(cpu) + rcu_spawn_cpu_nocb_kthread(cpu); + } } /* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */ -- 2.31.1.189.g2e36527f23