From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 96EE2346FB5; Fri, 3 Jul 2026 14:56:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783090619; cv=none; b=KPGtFN0uhTw5bbCjbtsVEMuZAcxVmq/N9f/6iQYH/XzuNPYblvnZlDrO5IJ0xk3bqnEn8nqKwvM17s/+MtOI60YOMBBtMNRXVrpu8e2OCMEde38wyGRlVoJXJ+wkPUVwetG/lCCFpNm8CVhEEzxLQOYJt4ZK8cUckvgg5H5bnGM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783090619; c=relaxed/simple; bh=M1GUwna4gUioTCqZ3drFdqpZNEmjfWoGLhtUB9HEaF0=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=M1LhMb6kc4rhlkKcHwNJtiMZTgg6sh6O6rVMilQgl2qI9CZxu0aQ3cD2cvw93U5Lf4Zqpi+oPeCz1qgMF8Kg+Ngdx0PR2e7PN7daRQERSjwJyHz+8gvJn+t1vJDruREZMw/kwq7L64aP0CGOBz5l04MRIykaGaiaXJgxgP2Bl38= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=N8pSrHEf; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=n1QKGeso; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="N8pSrHEf"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="n1QKGeso" 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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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