From nobody Wed Nov 27 14:20:05 2024 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 C18FF19DF66; Wed, 9 Oct 2024 18:05:11 +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=1728497111; cv=none; b=Qw6KwTB+gux4dGwFYMMUZYYoLPl1hk8iVtQAAP1QQIz2VmJHKQUbuxmL8+rbrFpZF+mVh/QglLtTQ6u5KuZlD83RixYkxwdiUEy56RqOi8i0q5TtUN19tb6R2t4mbdMOTVo4Lehw/+j5cDtkvnNmWSuPuoiqzqH+sOFfQ1a7T/g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728497111; c=relaxed/simple; bh=LXGw5NZfIRWF05WERyYwMt48zLZsjeoEitaRbfqAzcI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=gu25mGNqOv5eqhctsXWHsd5oA603TUSQKIO16FP1oMk5vBFqnpJ1Zpz+f3vsGT+APhxofPTaGVbSSJ/nlSzof1nPNa9e9VuWMAfUMvrORudWtN6W42PO6bJVJqzFZfuHkB1FO1BGlwhXKF4tQ/1ksU37oYva/fD9G/4rRvuBl0c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c2H09bcq; 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="c2H09bcq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A051C4CECF; Wed, 9 Oct 2024 18:05:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728497111; bh=LXGw5NZfIRWF05WERyYwMt48zLZsjeoEitaRbfqAzcI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c2H09bcquVszeNTbbwLGvSRoTwW5NnJAkcpb8ZXUJA0IHbjvKgY3310QyyONKr+dq 4WYyZQIjbN/yq23dNmfr4lRC/XTojre+vsa37/zMN8MSI97UHczXq21VmwdU4u4DTb j8RXIb3mBQAxONX2px8eIoYSt35K17bWjsaRMFHx+4ttZ/kG6rnsV7XCggtcgEgO5b 4j4ptCTvyhjIIzgUN6LNqnDyc4pnP7j/qVwRrBKpMAt6WHqcNgyBTs9Sr1J+IuJAUY aoiNv9n9+pbyWM0lLyjq5TY7Xd27FirsABBFmgWpRu57Y1ZXXA0qcKqFoqjHJcZI7h sP1nIQEr/8sOw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id F2DC8CE0BB1; Wed, 9 Oct 2024 11:05:10 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu 3/3] rcu: Finer-grained grace-period-end checks in rcu_dump_cpu_stacks() Date: Wed, 9 Oct 2024 11:05:09 -0700 Message-Id: <20241009180509.778133-3-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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. Signed-off-by: Paul E. McKenney --- 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 9d79133377ff6..8994391b95c76 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; =20 rcu_for_each_leaf_node(rnp) { - if (gp_seq !=3D 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 !=3D 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(); } } --=20 2.40.1