Messages in this thread | | | Date | Mon, 8 Jun 2009 10:48:07 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase |
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* Dave Young <hidave.darkstar@gmail.com> wrote:
> On Mon, Jun 8, 2009 at 4:28 PM, Andrew Morton<akpm@linux-foundation.org> wrote: > > On Mon, 8 Jun 2009 10:14:39 +0200 Ingo Molnar <mingo@elte.hu> wrote: > > > >> > >> * 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. > >> > > >> > 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 <hidave.darkstar@gmail.com> > >> > --- > >> > 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.
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