Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755003AbZFHIsS (ORCPT ); Mon, 8 Jun 2009 04:48:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752599AbZFHIsK (ORCPT ); Mon, 8 Jun 2009 04:48:10 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:43905 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752455AbZFHIsJ (ORCPT ); Mon, 8 Jun 2009 04:48:09 -0400 Date: Mon, 8 Jun 2009 10:48:07 +0200 From: Ingo Molnar To: Dave Young Cc: Andrew Morton , Linux Kernel Mailing List , Linus Torvalds Subject: Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase Message-ID: <20090608084807.GE6372@elte.hu> References: <20090608081439.GB6372@elte.hu> <20090608012845.9c428525.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.18 (2008-05-17) X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.5 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3180 Lines: 76 * Dave Young wrote: > On Mon, Jun 8, 2009 at 4:28 PM, Andrew Morton wrote: > > On Mon, 8 Jun 2009 10:14:39 +0200 Ingo Molnar wrote: > > > >> > >> * Dave Young wrote: > >> > >> > Add a halt_delay module parameter in printk.c used to read the > >> > printk messages in halt/poweroff/restart phase, delay each printk > >> > messages by halt_delay milliseconds. It is useful for debugging if > >> > there's no other way to dump kernel messages that time. > >> > > >> > The halt_delay max value is 65535, default value is 0, change it > >> > by: > >> > > >> > echo xxx > /sys/module/printk/parameters/halt_delay > >> > > >> > Signed-off-by: Dave Young > >> > --- > >> > Documentation/kernel-parameters.txt | ? ?5 +++++ > >> > kernel/printk.c ? ? ? ? ? ? ? ? ? ? | ? 17 +++++++++++++++++ > >> > 2 files changed, 22 insertions(+) > >> > > >> > --- linux-2.6.orig/kernel/printk.c ?2009-06-08 13:55:35.000000000 +0800 > >> > +++ linux-2.6/kernel/printk.c ? ? ? 2009-06-08 13:56:23.000000000 +0800 > >> > @@ -250,6 +250,22 @@ static inline void boot_delay_msec(void) > >> > ?} > >> > ?#endif > >> > > >> > +/* msecs delay after each halt/poweroff/restart phase printk, > >> > + unsigned short is enough for delay in milliseconds */ > >> > +static unsigned short halt_delay; > >> > + > >> > +static inline void halt_delay_msec(void) > >> > +{ > >> > + ? if (unlikely(halt_delay == 0 || !(system_state == SYSTEM_HALT > >> > + ? ? ? ? ? ? ? ? ? ? ? ? ? || system_state == SYSTEM_POWER_OFF > >> > + ? ? ? ? ? ? ? ? ? ? ? ? ? || system_state == SYSTEM_RESTART))) > >> > + ? ? ? ? ? return; > >> > >> This is a tiny bit ugly (and goes into the vprintf path) but i can > >> see no other way either - a system_state > SYSTEM_RUNNING check > >> would needlessly include the suspend-to-disk state (which we dont > >> want to include here). > >> > >> In theory we could turn system_state into a bitmask and have a > >> print_delay_mask check instead of these flags ... but that is a far > >> wider change and i'm not sure it's a net step forwards. > >> > >> I've applied your patch to tip:core/printk with small edits to the > >> changelog - Linus & Andrew is Cc:ed, should they have any > >> objections. > > > > Could we not put just a single delay in there, immediately prior to halting, > > restarting or poweroffing? > > But, then prink messages will still flush too fast for us to see > the detail. Plus often there's a loop in architecture code that tries various methods of reboot. We dont know which one works - and any of them could produce warning messages. (and this happened a number of times in the past) So this would mean having to find up to a hundred of 'reboot now' places in a two dozen architectures (and keeping them all maintained ongoing as well). Does not seem like a good choice to me. Ingo -- 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/