Messages in this thread | | | Date | Tue, 2 Jun 2009 12:56:09 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] printk: add halt_delay parameter for printk delay in halt phase |
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* Dave Young <hidave.darkstar@gmail.com> 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 <hidave.darkstar@gmail.com> > --- > 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
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