From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757686AbaDWSRx (ORCPT ); Wed, 23 Apr 2014 14:17:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:57695 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752500AbaDWSRv (ORCPT ); Wed, 23 Apr 2014 14:17:51 -0400 Date: Wed, 23 Apr 2014 11:17:50 -0700 From: Andrew Morton To: Jan Kara Cc: One Thousand Gnomes , LKML , pmladek@suse.cz, Frederic Weisbecker , Steven Rostedt Subject: Re: [PATCH 8/8] printk: Add config option for disabling printk offloading Message-Id: <20140423111750.88ad799bb271a1fe0bed119f@linux-foundation.org> In-Reply-To: <20140423110847.GB17824@quack.suse.cz> References: <1395770101-24534-1-git-send-email-jack@suse.cz> <1395770101-24534-9-git-send-email-jack@suse.cz> <20140326172332.5f1e1bfb@alan.etchedpixels.co.uk> <20140326192815.GC18118@quack.suse.cz> <20140418115438.1e65e07af17e3ba6d7c554db@linux-foundation.org> <20140422112259.5f106a44@alan.etchedpixels.co.uk> <20140423110847.GB17824@quack.suse.cz> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 23 Apr 2014 13:08:47 +0200 Jan Kara wrote: > > If you want reliable crash logging then we need to be able to set a > > printk level mask per console and just set the serial console for > > "crit/err" and the queue console for the rest, with a 'cat > > >/dev/ttywhatever' running if this feature was in use ? > Ok, now I understand. Thanks for an interesting idea. IMO people > definitely need messages logged directly into serial console when e.g. oops > is happening because very likely they won't get logged to disk and even > userspace won't have a chance to run and copy messages to the serial > console. Plus for useful softlockup reports or oops messages you need also > the KERN_NOTICE and KERN_INFO messages - stack traces, cpu numbers, process > information - all this is printed with these levels. > > These obvious places could be changed to print with lower log level I > assume but still I'm somewhat worried that some KERN_INFO messages that > would be useful for debugging a crash won't make it to console before the > crash happens. > > But if both you and Andrew think that the above problems are smaller than > the complexity connected with printk offloading, I can give it a try. > Andrew? I'm curious about the idea of writing a new(?) console driver which the problematic machines can use. The problem of course will be in sizing the driver's queue. Perhaps we can have a driver which uses a huge queue, temporarily use that driver during boot then switch over to a conventional console driver?