linux-kernel - Re: [PATCH 4/4 v2] watchdog: configure nmi watchdog period based on watchdog

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Message-ID: <20110518083936.GF14805@elte.hu>
Date:	Wed, 18 May 2011 10:39:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mandeep Singh Baines <msb@...omium.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	Don Zickus <dzickus@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH 4/4 v2] watchdog: configure nmi watchdog period based on
 watchdog_thresh


* Mandeep Singh Baines <msb@...omium.org> wrote:

> Ingo Molnar (mingo@...e.hu) wrote:
> > 
> > * Mandeep Singh Baines <msb@...omium.org> 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.

Thanks,

	Ingo
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