From patchwork Tue Nov 12 14:37:11 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Frederic Weisbecker X-Patchwork-Id: 13872321 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C93D8200133; Tue, 12 Nov 2024 14:37:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731422247; cv=none; b=Cgl52mhqn4Gy5qkDuFY1djEaXW/3anjnclgybaGg9qD00LanWpuRvz92vqLM1h83rkhW1LLwxxQJSdTXLE7fqG3yOfanzNAMOlQYSDH7Wq0HTtVi1kb3K8Z1ctDEa236zicqaplrb6LZWDG46QYOVVaxMWuvFqaPq3s7jhSTZb8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731422247; c=relaxed/simple; bh=2S3GF9YgOUVpSAFE9yXBXJbkzVZbHzXUYGcIPmCPbZ4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lemDlobhfEwA5M6n33CGZbTn1SEEtzy/WrwZKrVSt2a/KctboSYY/zGsey2r7R0ORTs7D9qfRnWS6FGw0/lZ3Js8Phk6hKkAN/7xNbSpuANxGOQqKKpSwk05q3qj0iS4ilZ2vAMko9FRms6NwA6pMm4laBqhxnWW6qF5HAPtgIo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=E2Mn6xzC; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="E2Mn6xzC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D6B26C4CED0; Tue, 12 Nov 2024 14:37:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731422247; bh=2S3GF9YgOUVpSAFE9yXBXJbkzVZbHzXUYGcIPmCPbZ4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=E2Mn6xzCC22m1WxtxUGNvC2lSrvLRNlRgjRuhrdlOyrUOIZnLSVP/Yo8k6WcGze6j 9Ka9JBu64D+JMdH1PueyIoUUZ7Ewhn+9XydE01xmBhQSbYrvI14/RUqaLpGiMUfZSo ICkvifnHUUskFbqBVJBqCmnrYzAlAc12Scwz1WFNzzQbJRRzYNmSM3btCBo4Imvvzu NyK0w8YG1qwmtjE2AaU2W/InanaH9tRBAsxwvsjYCC4vrnInjCKMsYJXngjaxmDOzu r0UJhz50sJdUeYTgJE9dwar3Kmcg4s0z/wsFvHzjx3PXfMyvIqI7vg5TkA8whm/jXn mvaFriSbpmkBQ== From: Frederic Weisbecker To: LKML Cc: "Paul E. McKenney" , Boqun Feng , Joel Fernandes , Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , Neeraj Upadhyay , Steven Rostedt , Uladzislau Rezki , Zqiang , rcu , Frederic Weisbecker Subject: [PATCH 3/3] rcu: Finer-grained grace-period-end checks in rcu_dump_cpu_stacks() Date: Tue, 12 Nov 2024 15:37:11 +0100 Message-ID: <20241112143711.21239-4-frederic@kernel.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20241112143711.21239-1-frederic@kernel.org> References: <20241112143711.21239-1-frederic@kernel.org> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: "Paul E. McKenney" This commit pushes the grace-period-end checks further down into rcu_dump_cpu_stacks(), and also uses lockless checks coupled with finer-grained locking. The result is that the current leaf rcu_node structure's ->lock is acquired only if a stack backtrace might be needed from the current CPU, and is held across only that CPU's backtrace. As a result, if there are no stalled CPUs associated with a given rcu_node structure, then its ->lock will not be acquired at all. On large systems, it is usually (though not always) the case that a small number of CPUs are stalling the current grace period, which means that the ->lock need be acquired only for a small fraction of the rcu_node structures. [ paulmck: Apply Dan Carpenter feedback. ] Signed-off-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) Signed-off-by: Frederic Weisbecker --- kernel/rcu/tree_stall.h | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index b530844becf8..925fcdad5dea 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -342,20 +342,24 @@ static void rcu_dump_cpu_stacks(unsigned long gp_seq) struct rcu_node *rnp; rcu_for_each_leaf_node(rnp) { - if (gp_seq != data_race(rcu_state.gp_seq)) { - pr_err("INFO: Stall ended during stack backtracing.\n"); - return; - } printk_deferred_enter(); - raw_spin_lock_irqsave_rcu_node(rnp, flags); - for_each_leaf_node_possible_cpu(rnp, cpu) + for_each_leaf_node_possible_cpu(rnp, cpu) { + if (gp_seq != data_race(rcu_state.gp_seq)) { + printk_deferred_exit(); + pr_err("INFO: Stall ended during stack backtracing.\n"); + return; + } + if (!(data_race(rnp->qsmask) & leaf_node_cpu_bit(rnp, cpu))) + continue; + raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { if (cpu_is_offline(cpu)) pr_err("Offline CPU %d blocking current GP.\n", cpu); else dump_cpu_task(cpu); } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } printk_deferred_exit(); } }