Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757023AbZFBK4Z (ORCPT ); Tue, 2 Jun 2009 06:56:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755601AbZFBK4L (ORCPT ); Tue, 2 Jun 2009 06:56:11 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:48820 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755301AbZFBK4L (ORCPT ); Tue, 2 Jun 2009 06:56:11 -0400 Date: Tue, 2 Jun 2009 12:56:09 +0200 From: Ingo Molnar To: Dave Young Cc: Linux Kernel Mailing List Subject: Re: [PATCH] printk: add halt_delay parameter for printk delay in halt phase Message-ID: <20090602105609.GA9182@elte.hu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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: 2761 Lines: 81 * 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. nice idea! We frequently have kernel-death warnings/messages that scroll off too fast and which cannot be captured. > halt_delay default value is 0, change it by: > > echo xxx > /sys/module/printk/parameters/halt_delay > > Signed-off-by: Dave Young > --- > kernel/printk.c | 21 +++++++++++++++++++++ > lib/Kconfig.debug | 10 ++++++++++ > 2 files changed, 31 insertions(+) > > --- linux-2.6.orig/kernel/printk.c 2009-04-09 16:23:03.000000000 +0800 > +++ linux-2.6/kernel/printk.c 2009-06-02 17:45:54.000000000 +0800 > @@ -250,6 +250,26 @@ static inline void boot_delay_msec(void) > } > #endif > > +#ifdef CONFIG_HALT_PRINTK_DELAY (this #ifdef is ugly - see below.) > +/* msecs delay after each halt/poweroff/restart phase printk */ > +static unsigned int halt_delay; > + > +static inline void halt_delay_msec(void) > +{ > + if (halt_delay == 0 || !(system_state == SYSTEM_HALT > + || system_state == SYSTEM_POWER_OFF > + || system_state == SYSTEM_RESTART)) > + return; > + > + mdelay(halt_delay); > > boot_delay_msec(); > + halt_delay_msec(); i think it should be done in boot_delay_msec() and the function should be renamed to print_delay_msec() or so. > preempt_disable(); > /* This stops the holder of console_sem just where we want him */ > --- linux-2.6.orig/lib/Kconfig.debug 2009-05-12 11:27:22.000000000 +0800 > +++ linux-2.6/lib/Kconfig.debug 2009-06-02 17:50:15.000000000 +0800 > @@ -647,6 +647,16 @@ config BOOT_PRINTK_DELAY > BOOT_PRINTK_DELAY also may cause DETECT_SOFTLOCKUP to detect > what it believes to be lockup conditions. > > +config HALT_PRINTK_DELAY > + bool "Delay halt/poweroff/restart printk message by N milliseconds" > + depends on DEBUG_KERNEL && PRINTK && SYSFS > + default n > + help > + This build option allows you to read kernel messages in > + halt/poweroff/restart phase by inserting a short delay after > + each one. The delay is specified in milliseconds on the > + module parameter: /sys/module/printk/halt_delay. No need for a Kconfig option - this should be an unconditional feature like boot-delay. This will further simplify the patch and will get rid of that ugly #ifdef. 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/