Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase

[Dave Young <hidave.darkstar@gmail.com>]

On Mon, Jun 8, 2009 at 4:58 PM, Ingo Molnar<mingo@elte.hu> wrote:
>
> * 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.

Fine.

>
>        Ingo
>



-- 
Regards
dave