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    SubjectRe: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase
    On Tue, 9 Jun 2009 09:01:19 +0800 Dave Young <hidave.darkstar@gmail.com> wrote:

    > 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?

    sysfs is OK, if there's a logical place for it. /sys/kernel/, I suppose.

    > without system_state testing we will have to consider the NMI watchdog
    > and softlockup issue.

    Yup.




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