Re: [PATCH] hangcheck-timer is broken on x86

[Joel Becker]

On Sat, Mar 27, 2010 at 06:51:01PM -0400, Yury Polyanskiy wrote:
> >        It's OK to tell hangcheck-timer users that suspend is not
> > allowed.  After all, you're running something that you don't want to see
> > hang.
> 
> Joel, what I am saying is exactly the opposite: it is totally ok to
> suspend-resume with hangcheck-timer (jiffies are stopped and so is
> getrawmonotonic() when system suspended).

	Nope.  The point of hangcheck-timer is that it reboots should
the system not be running for a certain amountof time.  If
suspend-resume is allowed, a system can resume after days and think it
wasn't more than a second.  hangcheck-timer will not know to reboot.

> >        Is there a clock in the system that is a true wallclock?  I'm
> > guessing, since getrawmonotonic() is get_cycles() based, that it doesn't
> > provide accurate time in the face of cpufreq changes.  Is that true?
> 
> Of course, getrawmonotonic accounts for cpufreq changes (see
> arch/x86/kernel/tsc.c:time_cpufreq_notifier()).

	Excellent!  That's a definite improvement over raw get_cycles().

Joel

-- 

Life's Little Instruction Book #182

	"Be romantic."

Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@xxxxxxxxxx
Phone: (650) 506-8127
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/