Messages in this thread | | | Date | Tue, 9 Jun 2009 09:01:19 +0800 | Subject | Re: [PATCH v3] printk: add halt_delay parameter for printk delay in halt phase | From | Dave Young <> |
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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. >
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