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

* 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?

Sparc64 does too IIRC.

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

Consolidatig with the existing boot delay implementation was one of
my first suggestions.

The /proc thing definitely makes sense - the boot option was just
symmetry to the existing boot-delay approach.

I've unapplied this patch - i agree that it needs a bit more work
and i dont want to hold up other changes in the core/printk branch.

Ingo


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