Re: [PATCH 1/6] UML - Deal with host time going backwards

[Andrew Morton <akpm@linux-foundation.org>]

On Tue, 03 Jun 2008 20:52:18 +0100
Nix <nix@esperi.org.uk> wrote:

> On 3 Jun 2008, Daniel Hazelton said:
> 
> > On Tuesday 03 June 2008 03:32:11 pm Andrew Morton wrote:
> >> On Tue, 3 Jun 2008 15:02:35 -0400
> >>
> >> Jeff Dike <jdike@addtoit.com> wrote:
> >> > Protection against the host's time going backwards - keep track of the
> >> > time at the last tick and if it's greater than the current time, keep
> >> > time stopped until the host catches up.
> >>
> >> Strange.  What would cause the host's time (or at least UML's perception
> >> of it) to go backwards?
> >
> > A wild guess would be that the UML process is running "fast" at some point and 
> > its expectation of the host's time is skewed forward because of that.
> 
> Quite so. Simply running ntp on the host (in slew-only mode, no less!) 
> can cause this.
> 
> > Another possibility is that the hosts clock got reset between the times UML 
> > has checked it and the correction was a negative one.
> 
> That too.
> 

So if I change the host's time by an hour, the time will not advance at all
on the guest for the next hour? Sounds suboptimal :)

I suppose the guest should be running an ntp client synced to something
sane anyway?