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    SubjectRe: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase
    On Tue, Jun 9, 2009 at 9:01 AM, Dave Young<> wrote:
    > On Tue, Jun 9, 2009 at 5:39 AM, Andrew Morton<> wrote:
    >> On Mon, 8 Jun 2009 19:15:01 +0200
    >> Ingo Molnar <> 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

    And, if making it a general feature, I think maybe delay per screen
    (ie. 25 lines) is a good way.

    >> 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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