Re: [PATCH 4/4 v2] watchdog: configure nmi watchdog period based onwatchdog_thresh

From: Ingo Molnar
Date: Wed May 18 2011 - 04:39:53 EST

* Mandeep Singh Baines <msb@xxxxxxxxxxxx> wrote:

> Ingo Molnar (mingo@xxxxxxx) wrote:
> >
> > * Mandeep Singh Baines <msb@xxxxxxxxxxxx> wrote:
> >
> > > Before the conversion of the NMI watchdog to perf event, the watchdog
> > > timeout was 5 seconds. Now it is 60 seconds. For my particular application,
> > > netbooks, 5 seconds was a better timeout. With a short timeout, we
> > > catch faults earlier and are able to send back a panic. With a 60 second
> > > timeout, the user is unlikely to wait and will instead hit the power
> > > button, causing us to lose the panic info.
> >
> > That's an interesting observation. Have you been able to measure/observe this
> > effect somehow, or do you presume that users find 60 seconds too long?
> >
> Mostly intuition. There is a threshold beyond which the user will hit
> the power button. Not sure if its 20 seconds or 20 minutes. My feeling
> was that the 1 minute was too long.
> For a user experience perspective, a quick reboot also seems like a better
> experience than a one minute hang. Our systems boot in 8 seconds and restore
> the previous session so a reboot is almost not noticable.

Indeed you definitely want it configurable and have the delay down to 5 or 10
seconds, to correlate it with your boot delay.

Personally i consider any hang over 1 second annoying so you might want to work
on that 8 seconds boot time some more, it's too long ;-)

And any kernel code running with more than 1 second irqs off is a bug, plain
and simple.


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