Messages in this thread | | | Date | Mon, 8 Jun 2009 16:42:29 +0800 | Subject | Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase | From | Dave Young <> |
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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.
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