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

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Date:	Mon, 8 Jun 2009 16:56:39 +0800
From:	Dave Young <hidave.darkstar@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v3] printk: add halt_delay parameter for printk delay in 
	halt phase

On Mon, Jun 8, 2009 at 4:46 PM, Ingo Molnar<mingo@...e.hu> wrote:
>
> * Dave Young <hidave.darkstar@...il.com> wrote:
>
>> On Mon, Jun 8, 2009 at 4:14 PM, Ingo Molnar<mingo@...e.hu> wrote:
>> >
>> > * Dave Young <hidave.darkstar@...il.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@...il.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.

>
>        Ingo
>



-- 
Regards
dave
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