Messages in this thread | | | Date | Mon, 8 Jun 2009 10:58:19 +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 4:46 PM, Ingo Molnar<mingo@elte.hu> wrote: > > > > * Dave Young <hidave.darkstar@gmail.com> wrote: > > > >> On Mon, Jun 8, 2009 at 4:14 PM, 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). > >> > >> Can we move suspend-to-disk before halt state? > > > > Yes, we could do that - if all system_state uses are checked for > > side-effects - in particular comparisons. We have a few places that > > do 'if (system_state > SYSTEM_RUNNING)' - to designate 'shutdown > > state'. Now, if we have any use of > SYSTEM_SHUTDOWN that might > > break from such a reordering. > > > > I wouldnt expect such usage really, but it has to be checked. That > > would make this patch quite a bit cleaner. > > > > Mind sending a followup delta patch with this cleanup? > > I'm glad to check the system_state usage, then write a followup patch.
I'd also suggest to add a comment to the constants, to make sure that when new system states are added, the ordering assumptions are not broken.
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