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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 9756AC43458 for ; Fri, 3 Jul 2026 14:57:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Subject:Cc:To: From:Date:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=XhzwfdKhTuMTAOcT4iD8RFsrIkmNOcMgyrA0M5/090s=; b=Xtip6tZH6c9RYcnHtlAgaPvNMD kFoCd+XPLQFKT1ARnQsxbMJVlmAISFJNwbUYPcx56sB3DBllVpkcglgHk2i9BAqjrKX++o9Mf5A7+ 02WwdKQ4xtn7KTpxF5QB6yUZzEX0GLUyxEYvtZmrqNtUvxnffPxlDSaM2OqBiLv4Q4lmAKdmW6KCB y0o+ZshJWa8F3vyv3itft41Jlu7i60sC6iSAM7oH3vAU+AX9y6yxLC0E4YN65ov/FGE8ubfWRgulG SrH21faGS/k9JacuYcDOZm1tYbYZeMeV6nTjugG7RnrzjqJxWJ7/GQR3zKgHZloY3nsE97xp6tIAa M3UM+Rjg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wffKB-00000007L46-0Zzv; Fri, 03 Jul 2026 14:57:03 +0000 Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wffK8-00000007L3M-3IL9; Fri, 03 Jul 2026 14:57:02 +0000 Date: Fri, 3 Jul 2026 16:56:54 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1783090616; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XhzwfdKhTuMTAOcT4iD8RFsrIkmNOcMgyrA0M5/090s=; b=N8pSrHEfmQ0nIHyuLnBq7B9PeE26JJ6i6JuUNkB6AErxg1ZsJZrYjXpUiRBwV6WTy/kArw gLrBYbX5ujE+pMhJ+nz/vQIuptan7+PiNQr91clPODzPGyuOKXMAT4jBJmCAZTBgW6rwO0 WTnkL3W5JRHjS4kJxy6nSRgDh8vcgGISPieH12Rmd8dhkxiwSh2m6R0k8h3P1g6LLWMZ9q qU10psMDI6xYcKMsz/PDAcWF5XlwCFt1O1jVVeWkpED0utDp/dJU6w4P90MreD/L6Ir5Cw /pp4RYdshAADZuypWEakuuPcxoIxO8Ezm927mKygUFM+/DTcGDll/4WpQO+QHw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1783090616; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XhzwfdKhTuMTAOcT4iD8RFsrIkmNOcMgyrA0M5/090s=; b=n1QKGesoiWFZPHP7w3oYq8LG0f80nKkIcc2D5Au3fKdGTMx5zz0lcAroYrnAoT2K0UOqdd F2VnPZHabXxb0PAw== From: Benedikt Spranger To: Andrew Murray Cc: Jonathan Corbet , Shuah Khan , Russell King , Florian Fainelli , Broadcom internal kernel review list , Ray Jui , Scott Branden , Petr Mladek , Steven Rostedt , John Ogness , Sergey Senozhatsky , Andrew Morton , Sebastian Andrzej Siewior , Clark Williams , Randy Dunlap , Linus Torvalds , Greg Kroah-Hartman , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, linux-rt-devel@lists.linux.dev Subject: Re: [PATCH v2 3/4] printk: nbcon: move printk_delay to console emiting code Message-ID: <20260703165654.71be8707@mitra> In-Reply-To: <20260630-deprecate_boot_delay-v2-3-f9883d36aa4b@thegoodpenguin.co.uk> References: <20260630-deprecate_boot_delay-v2-0-f9883d36aa4b@thegoodpenguin.co.uk> <20260630-deprecate_boot_delay-v2-3-f9883d36aa4b@thegoodpenguin.co.uk> Organization: Linutronix GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260703_075700_995616_35F60A7D X-CRM114-Status: GOOD ( 12.72 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 30 Jun 2026 17:35:59 +0100 Andrew Murray wrote: > The printk_delay and boot_delay features are helpful for debugging > as kernel output can be slowed down during boot allowing messages to > be seen before scrolling off the screen, or to correlate timing > between some physical event and console output. By now, it slows down the boot process, which is the handy part of that feature. > However, since the introduction of nbcon and the legacy printer thread > for PREEMPT_RT kernels, printk records are now emited to the console > asynchronously to the caller of printk. Thus, any printk delay added > by boot_delay/printk_delay continues to slow down the calling process > but may not have any impact to the rate in which records are emited > to the console. Using this feature to slow down the boot/suspend/resume process and implicit make printk() happen, is the usefull part of that feature. Imagine this sequence (which hit me on suspend/resume on i.MX after shutting down all secondary CPUs) printk("A"); (do some stuff) printk("B"); read from peripheral --> system got stuck here since peripheral was not clocked or powered or both any more. The delay (and later on a ugly patch to make printk() synchrounous) helped to locate where the failed access happend. JTAG did not help, since the CPU got stuck --> no JTAG communication to that CPU. With your purposed change you *may* see "A", but never "B". Quite challenging... So please leave the delay on the calling side - it is helpfull there. Regards Bene Spranger