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 16:37:35 +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 4:14 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?

>
> 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.
>
>        Ingo
>



-- 
Regards
dave
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