Re: HPET regression in 2.6.26 versus 2.6.25 -- question about NMI watchdog

Re: HPET regression in 2.6.26 versus 2.6.25 -- question about NMI watchdog

[David Witbrodt]

> > I found something very interesting about the commit that first causes 
> > the lockup (3def3d6d...), and the very next commit (1e934dda...) -- if 
> > I checkout 1e94... and try to revert the changes made in 3def..., the 
> > kernel freezes in spite of the revert.
> > 
> > Because of this, I would conclude that your patch for 2.6.27-rc3 was 
> > doomed before you began, and we should look more carefully at the 
> > commits from February instead of trying to revert at the 2.6.27 HEAD.
> 
> i'm still wondering whether we could try to figure out something about 
> the nature of the hard lockup itself.
> 
> Have you tried to activate the NMI watchdog? It _usually_ works fine if 
> you use a boot option along the lines of:
> 
>    "lapic nmi_watchdog=2 idle=poll"

I have to go to work for a few hours right now, but will try this out when
I get home.  (Actually, I'm late for work as I type this... but I have my
priorities straight!  ;)

Quick question:  a quick browse of 'Documentation/nmi_watchdog.txt' suggests
that I should use "nmi_watchdog=1", since I have SMP (CPU = Athlon 64 X2,
with CONFIG_SMP=y).  Should I follow your suggestion later, or follow the
recommendation of the 'nmi_watchdog.txt' doc?


Much thanks,
Dave W.

Re: HPET regression in 2.6.26 versus 2.6.25 -- question about NMI watchdog

[Ingo Molnar]

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* David Witbrodt <dawitbro@sbcglobal.net> wrote:

> Quick question: a quick browse of 'Documentation/nmi_watchdog.txt' 
> suggests that I should use "nmi_watchdog=1", since I have SMP (CPU = 
> Athlon 64 X2, with CONFIG_SMP=y).  Should I follow your suggestion 
> later, or follow the recommendation of the 'nmi_watchdog.txt' doc?

you could try both, starting with nmi_watchdog=2 - and trying 
nmi_watchdog=1 if that doesnt work. The problem with nmi_watchdog=1 is 
that it disables high-res timers. (because it has to - it piggy-backs on 
the back of a periodic timer interrupt)

you might even want to test the NMI watchdog with an intentional 
user-space hard lockup - with the attached lockupcli.c program. 
(Warning: if you run it as root it will really lock up your box hard. 
Run it from a VGA text mode console to see any console messages.)

	Ingo

[-- Attachment #2: lockupcli.c --]
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main ()
{
	iopl(3);
	for (;;) asm("cli");
}