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    SubjectRe: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase
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    On Tue, Jun 9, 2009 at 5:39 AM, Andrew Morton<akpm@linux-foundation.org> wrote:
    > On Mon, 8 Jun 2009 19:15:01 +0200
    > Ingo Molnar <mingo@elte.hu> wrote:
    >
    >> > questions: is it possible for interrupts to be disabled at this
    >> > time? If so, can we get an NMI watchdog hit?
    >>
    >> no, we generally turn off the nmi watchdog during shutdown, disable
    >> the lapic and io-apic, etc.
    >
    > Is x86 the only architecture which implements an NMI watchdog?
    >
    >> > Is the softlockup detector still running and if so, can it
    >> > trigger?
    >>
    >> in (non-emergency) reboot, last i checked, we stopped all other CPUs
    >> first, and then killed the current one. There's no chance for the
    >> watchdog thread to run.
    >
    > OK, but...  See below.
    >
    >> Anyway ... you seem to be uncomfortable about this patch - should i
    >> delay it for now to let it all play out? We are close to the merge
    >> window.
    >
    > I'm OK - I'm just bouncing ideas and questions off you guys, to make sure
    > that we've thought this through all the way.
    >
    > Here's another: why is it a boot option rather than a runtime-tunable?
    > A /proc tweakable is generally preferable because it avoids the
    > oh-crap-i-forgot-to-edit-grub.conf thing.  And we could perhaps then
    > remove all those system_state tests: userspace sets printk_delay
    > immediately prior to running halt/reboot/etc?

    Andrew, thanks your comments.
    I original intention is to use not boot options but sysfs interface.
    Do you perfer proc?
    without system_state testing we will have to consider the NMI watchdog
    and softlockup issue.

    >
    > Plus the feature becomes more general - perhaps there are use cases
    > where people want to slow down printks, such as: kernel goes oops, data
    > scrolls off, serial console/netconsole unavailable.  pause_on_oops is
    > supposed to help here but last time I tried it, it kinda didn't work,
    > plus pause_on_oops doesn't solve the data-scrolled-off problem.

    Seems make sense.

    >
    > Thirdly, if we do this as a general /proc/printk_delay thing, perhaps
    > it can be consolidated with the existing boot_delay= implementation.
    >



    --
    Regards
    dave
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