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 D8429C433FE for ; Tue, 23 Nov 2021 00:37:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232525AbhKWAk6 (ORCPT ); Mon, 22 Nov 2021 19:40:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:48438 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232024AbhKWAka (ORCPT ); Mon, 22 Nov 2021 19:40:30 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0D3FC60698; Tue, 23 Nov 2021 00:37:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1637627843; bh=7azNNyfiT4FsHaHwOV8p/mGYeehxgOPmaWnVHxJUcWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=iCm9sIbq0gmfEbs81iOk3eurDsTUV9XjsbCVllrdUvQA/3YQa2VvNCQB4Ag1poyDi ncSSeW6TBuMeQ5cNNV6+3csHUslluoISiX8tqKiJjMvcZQ2MgbcmSAnWnDcWUR29d4 pq7a7jiYGf8ojN+o45BbEdLhHmgQdYFlYLJR7V39cY2yRzEKXp/U4JwNoOgvvH/QoF fGoQoHWhkmemSCuMabCZxZ9Vffvps9gFb5XY1+UV38WBB+og7OlDvuH0ZjBY+rKBvj Mu4XxqDRuZD0q/Ej6i0WgqVO6aoY/bq/nb5YyYTOtYnJ03SVLI7VuBgETHXef9p6ik NYnMNOxomj+Xg== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Uladzislau Rezki , Neeraj Upadhyay , Boqun Feng , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH 3/6] rcu/nocb: Optimize kthreads and rdp initialization Date: Tue, 23 Nov 2021 01:37:05 +0100 Message-Id: <20211123003708.468409-4-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211123003708.468409-1-frederic@kernel.org> References: <20211123003708.468409-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently cpumask_available() is used to prevent from unwanted NOCB initialization. However if neither "rcu_nocbs=" nor "nohz_full=" parameters are passed but 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 with relying on a real initialization state instead. This also optimize kthreads creation, sparing iteration over all online CPUs when nocb isn't initialized. Signed-off-by: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes --- 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 e1cb06840454..d8ed3ee47a67 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); @@ -1159,13 +1163,17 @@ 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) @@ -1267,8 +1275,10 @@ 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). */ -- 2.25.1