Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757441AbZFHQbw (ORCPT ); Mon, 8 Jun 2009 12:31:52 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756111AbZFHQbp (ORCPT ); Mon, 8 Jun 2009 12:31:45 -0400 Received: from smtp1.linux-foundation.org ([140.211.169.13]:56731 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756033AbZFHQbp (ORCPT ); Mon, 8 Jun 2009 12:31:45 -0400 Date: Mon, 8 Jun 2009 09:26:07 -0700 From: Andrew Morton To: Ingo Molnar Cc: Dave Young , Linux Kernel Mailing List , Linus Torvalds Subject: Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase Message-Id: <20090608092607.8b331bf0.akpm@linux-foundation.org> In-Reply-To: <20090608084807.GE6372@elte.hu> References: <20090608081439.GB6372@elte.hu> <20090608012845.9c428525.akpm@linux-foundation.org> <20090608084807.GE6372@elte.hu> X-Mailer: Sylpheed 2.4.8 (GTK+ 2.12.5; x86_64-redhat-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 Content-Length: 3761 Lines: 88 On Mon, 8 Jun 2009 10:48:07 +0200 Ingo Molnar wrote: > > * 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. Only if there are so many unlogged messages that they scroll of the screen. Is that the case? > 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. > hm. If we need to actually capture all of those. questions: is it possible for interrupts to be disabled at this time? If so, can we get an NMI watchdog hit? Is the softlockup detector still running and if so, can it trigger? -- 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/