Re: setting jiffies as the clocksource stops time

[Daniel Walker <dwalker@mvista.com>]

On Thu, 2008-01-17 at 23:34 +0100, Jan Engelhardt wrote:
> On Jan 16 2008 13:20, Daniel Walker wrote:
> >On Thu, 2008-01-17 at 02:09 +0530, Balaji Rao wrote:
> >> Hi,
> >> 
> >> When i set jiffies as the current_clocksource, date(1) tells me
> >> that wallclock time has stopped, and soon after that, the system
> >> becomes unresponsive. This is not seen with CONFIG_NO_HZ disabled.
> >> 
> >> I wonder how can jiffies be used as a clocksource.. Its value
> >> depends on the tick and when we turn off ticks, we would stop
> >> incrementing jiffies and when we come come out of idle, we update
> >> the jiffies by reading the current_clocksource which now is
> >> 'jiffies', and hence jiffies wouldn't get updated. Could this be
> >> the explanation ?
> >
> >Your right, It can't be used as a clocksource with nohz , and the system
> >will refuse to automatically switch to it ..
> 
> I think that manually changing to jiffies by echoing into sysfs
> should also be prohibited.

Yeah, I wasn't suggesting we shouldn't prevent it .. However, there are
tons of way to kill your system by manual changing things ..

Daniel