From patchwork Thu Jan 16 20:02:38 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: 13942188 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 3ABBE23F269; Thu, 16 Jan 2025 20:02:42 +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=1737057762; cv=none; b=gnBaNt0REXU+6H68uFwZ132ur8Q6f6N7wrWMbMQnlq6MKJ62gLuwk6rImqCUMoZp3xDiTbKof7IyHMyAV2oErd57J2841ckP2QhSkGPiPjspOjluwO3hnF1rr1UPwTeQVUGjctK2UuoNxaEVk4BLM32K0DRLdBoXxBGDqUZj0MU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737057762; c=relaxed/simple; bh=nCzBiBHz3M2xxT1NTdXIMhRys/kvq/wbFX7EYoDah+g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=inuuzqddOIqOdtfULxIPZmQE1hKe2Kgt4okz7md3jlhwuuNmQNZ/EH+aYWZHmOLSUszAJWG4gQobib8UGVzTPBfzkSqtmaNxe6ETdCU5mNt0M/eCYPaS+oPOM+fVvy7vNhPc58lt2RaI99ppfnlXHoe0xlla+6PXHtT+UhrhYGI= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=kEcvtssV; 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="kEcvtssV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D2AA3C4CEE9; Thu, 16 Jan 2025 20:02:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1737057761; bh=nCzBiBHz3M2xxT1NTdXIMhRys/kvq/wbFX7EYoDah+g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kEcvtssV3oT38qFLKH/36T5Z2kPdhHLdBFij255x0R67OP5KNYWBp1/Yu5s8vMGMf wPVwQLxawWj8Zulkjv0+0v3SezcxrWly8FqsrkXQxBiZKqcCz8X+JkU2mrd5E1cdRd cQ13/84dD+OzyS4RW3tGwOOpsLjZxyqYLOosjhLPMQY4IKHojK++O9JUEeo7/3bBHW hTeJaxikTKpjC7htp4PhAjDsU2JScTjegjsvbyVzto/MDMryCbXOWZZhBRUV5iPxLA f3j9XIXvE6ioh4Z5Z0HpGnkYpkzjGOubAwmGkuvX996CY+qeXhhVtZyj7/fGRhjIrm GCuDNmI9v76mA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 349F7CE37C4; Thu, 16 Jan 2025 12:02:41 -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 6/7] rcu: Clarify RCU_LAZY and RCU_LAZY_DEFAULT_OFF help text Date: Thu, 16 Jan 2025 12:02:38 -0800 Message-Id: <20250116200239.3782374-6-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: 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 b9b6bc55185db..2bb22dac3b5a9 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"