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

    >
    > 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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