Re: [PATCH v2] NMI: fix NMI period is not correct when cpu frequency changes issue.

[Don Zickus <dzickus@redhat.com>]

On Mon, Apr 22, 2013 at 12:50:34AM +0000, Pan, Zhenjie wrote:
> > I believe it mattered to the Chrome folks. They want the watchdog to be as
> > tight as possible so the user experience isn't a hang but a quick reboot
> > instead.  They like setting the watchdog to something like 2 seconds.
> > 
> > There was a patch a few months ago that tried to hack around this issue and I
> > suggested this approach as a better solution.  I forgot what the original
> > problem was.  Perhaps someone can jump in and explain the problem being
> > solved (other than the watchdog isn't always 10 seconds)?
> > 
> > Cheers,
> > Don
> 
> Yes, I also think the period is important sometimes.
> As I mentioned before, the case I meet is:
> When the system hang with interrupt disabled, we use NMI to detect.
> Then it will find hard lockup and cause a panic.
> Panic is very important for debug these kind of issues.
> 
> But if cpu frequency change, the period will be 2 times, 3 times even more.(if cpu can down from 2.0GHz to 200MHz, will be 10 times, it's a very big deviation)
> This make watchdog reset happen before hard lockup detect.

So you are saying with the longer hard lockup delay, the iTCO_wdt is
firing before the hard lockup detector?

Cheers,
Don