From patchwork Thu Jan 30 18:49:24 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Paul E. McKenney" X-Patchwork-Id: 13954856 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 158BA1F03E8; Thu, 30 Jan 2025 18:49:28 +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=1738262968; cv=none; b=NnPa4xHWsxZLsvNJG6Pz6nXs4rV1dhWfV3Gdu5w4MeUZFy2HOGH3ueUVxq5WkAF1Cj4ontmuGonCLB63EPzdC2qOjf2gExch3Shl5ViZ34bhn5qzOJoD9sfaJBUAE38SsEN8qbkN1TtRLakfSH9MkC2YXuelVpTwQmvO3J/7qio= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738262968; c=relaxed/simple; bh=VydZE0P4L/LZcwHPe6EIAqUlXj2KVbd6m5WrTYx83ZM=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=AVPdS6m3Oh+geQ8SLADL4UvmSRel+ai+pAypSCyR4Q8O4dxlnA2HgJDhicr9AXutJen4yEWs+UyWz+ahnqpX6ekmTZQFvevOpnFbj40AJHfF6cRJ0tFvzy43jinXnmZW8uJjxL/HqhL0Nh22rg1V1Avc/lSakKCzLlnCoaY0dnI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=cf3dyeag; 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="cf3dyeag" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D93FAC4CEE4; Thu, 30 Jan 2025 18:49:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1738262967; bh=VydZE0P4L/LZcwHPe6EIAqUlXj2KVbd6m5WrTYx83ZM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cf3dyeagGO3lHsz3fzg9A13l+2SU9nM4ekQ3sbU3Jgxh1M3694mKQ1FCOgLwvK6ye xHt5pcpwi7Yjq9t0ekONsh04sN9QcUKOi3/Ky3vpQ+g/X0hYJVIEHCNZ+aRVRRp1Rp mY3QbrNhPQ7soGaB15oPM5IewP2b3ih1MLa8T4jtX1XYIv753xrjk6WLaYznLVqheU dPoM0VN47I/nPut3L3oBKgENiCgmMtlOKP4oozcDaGl8CqbQ+WEckjL0za+rt4oUGo 56vErVxpzKo7dnfaodY7HfQjhkh/SNZjfwoRa+eg1+KKQ282LYPuugsNBQUMV8R+O8 uOp9CFDqGB9pQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 36154CE37E0; Thu, 30 Jan 2025 10:49:27 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu v2 6/7] rcu: Clarify RCU_LAZY and RCU_LAZY_DEFAULT_OFF help text Date: Thu, 30 Jan 2025 10:49:24 -0800 Message-Id: <20250130184925.1651665-6-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: <851fd11f-6397-4411-983b-96f7234326d5@paulmck-laptop> References: <851fd11f-6397-4411-983b-96f7234326d5@paulmck-laptop> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 This commit wordsmiths the RCU_LAZY and RCU_LAZY_DEFAULT_OFF Kconfig options' help text. Signed-off-by: Paul E. McKenney --- kernel/rcu/Kconfig | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index b9b6bc55185d..2bb22dac3b5a 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -323,21 +323,27 @@ config RCU_LAZY depends on RCU_NOCB_CPU default n help - To save power, batch RCU callbacks and flush after delay, memory - pressure, or callback list growing too big. + To save power, batch RCU callbacks and delay starting the + corresponding grace period for multiple seconds. The grace + period will be started after this delay, in case of memory + pressure, or if the corresponding CPU's callback list grows + too large. - Requires rcu_nocbs=all to be set. + These delays happen only on rcu_nocbs CPUs, that is, CPUs + whose callbacks have been offloaded. - Use rcutree.enable_rcu_lazy=0 to turn it off at boot time. + Use the rcutree.enable_rcu_lazy=0 kernel-boot parameter to + globally disable these delays. config RCU_LAZY_DEFAULT_OFF bool "Turn RCU lazy invocation off by default" depends on RCU_LAZY default n help - Allows building the kernel with CONFIG_RCU_LAZY=y yet keep it default - off. Boot time param rcutree.enable_rcu_lazy=1 can be used to switch - it back on. + Build the kernel with CONFIG_RCU_LAZY=y, but cause the kernel + to boot with these energy-efficiency delays disabled. Use the + rcutree.enable_rcu_lazy=0 kernel-boot parameter to override + the this option at boot time, thus re-enabling these delays. config RCU_DOUBLE_CHECK_CB_TIME bool "RCU callback-batch backup time check"