Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754330AbZJZSD7 (ORCPT ); Mon, 26 Oct 2009 14:03:59 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753696AbZJZSD6 (ORCPT ); Mon, 26 Oct 2009 14:03:58 -0400 Received: from relay3.sgi.com ([192.48.152.1]:53340 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753623AbZJZSD5 (ORCPT ); Mon, 26 Oct 2009 14:03:57 -0400 Message-ID: <4AE5E48F.6020408@sgi.com> Date: Mon, 26 Oct 2009 11:03:59 -0700 From: Mike Travis User-Agent: Thunderbird 2.0.0.23 (X11/20090817) MIME-Version: 1.0 To: Andi Kleen CC: Ingo Molnar , Thomas Gleixner , Andrew Morton , Jack Steiner , Randy Dunlap , Steven Rostedt , Greg Kroah-Hartman , Frederic Weisbecker , Heiko Carstens , Robin Getz , Dave Young , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [PATCH 1/8] SGI x86_64 UV: Add limit console output function References: <20091023233743.439628000@alcatraz.americas.sgi.com> <20091023233746.128967000@alcatraz.americas.sgi.com> <87tyxmy6x6.fsf@basil.nowhere.org> In-Reply-To: <87tyxmy6x6.fsf@basil.nowhere.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3190 Lines: 77 Andi Kleen wrote: > Mike Travis writes: > >> With a large number of processors in a system there is an excessive amount >> of messages sent to the system console. It's estimated that with 4096 >> processors in a system, and the console baudrate set to 56K, the startup >> messages will take about 84 minutes to clear the serial port. >> >> This patch adds (for SGI UV only) a kernel start option "limit_console_ >> output" (or 'lco' for short), which when set provides the ability to >> temporarily reduce the console loglevel during system startup. This allows >> informative messages to still be seen on the console without producing >> excessive amounts of repetious messages. >> >> Note that all the messages are still available in the kernel log buffer. > > I've run into the same problem (kernel log being flooded on large number of CPU thread > systems). It's definitely not a UV only problem. Making such a option UV only > is definitely not the right approach, if anything it needs to be for everyone. I could use something like the MAXSMP config option to enable it...? > > Frankly a lot of these messages made sense for debugging at some point, > but really don't anymore and should just be removed. That they still go to the kernel log buffer means the messages are still available for debugging system problems. KDB has a kernel print option if you end up there before being able to use 'dmesg'. > > Also I don't like the defaults of on. It would be better to evaluate if > these various messages are really useful and if they are not just remove them. I believe most distros already do that by setting the loglevel argument (but I could be wrong since I haven't looked at too many of them.) > > For example do we really need the scheduler debug messages by default? This was the most painful message at Nasa (which has a 2k cpu system). It took well over an hour for these scheduler messages to print, just because we wanted to get some other DEBUG prints. > > Or do we really need to print the caches for each CPU at boot? The information > is in sysfs anyways and rarely changes (I added this originally on 64bit, > but in hindsight it was a bad idea) I was attempting not to decide whether each message was pertinent, only if it was redundant. > > I don't think it makes much sense to print more than 2-3 lines for each CPU boot > for example. That would still be 4 to 12 thousand lines of information which, as you say is available by other means. > > Also more work could be done to make CPU boot up less verbose without > sacrifying debuggability if something goes wrong. > > So please: > - Simply remove messages that don't make sense, no flag. > - Make the default non verbose. > - Minimize output in general, with just a few standard checkpoints so > that if there is a hang the developer still has some clue what went wrong. loglevel=4 does this quite nicely. ;-) Thanks, Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/