[libvirt] time: event poll may become un-triggerable after changing system clock.

Daniel P. Berrange berrange at redhat.com
Wed May 13 08:14:13 UTC 2015

On Wed, May 13, 2015 at 08:54:49AM +0800, zhang bo wrote:
> On 2015/5/12 16:56, Daniel P. Berrange wrote:
> > On Tue, May 12, 2015 at 04:14:37PM +0800, zhang bo wrote:
> >> So, Is there any other better solution? thanks in advance.
> > 
> > Simply don't change the system time by massive deltas. Libvirt is not going
> > to be the only app to be affected. As you mention it is going to hit the
> > pthread_cond_wait() call which will likely affect pretty much every single
> > non-trivial process running on the system. I'd expect other apps have much
> > the same problem with calculating poll sleeps too.
> > 
> > If you need to massively change the system time this should be done at
> > single user mode, or do a reboot. Once a system is running it should be
> > kept synced with NTPD which will only ever change system time in very
> > small increments and so once cause thsi problem.

> Would you please explain more about what "single user mode" mean here? and does "reboot" refers to
> "rebooting the os" or "rebooting the process libvirtd"?  I think it's "the process", right?

Single user mode is where you boot the OS such that you only have a
root shell running. No other processes are present. So you can safely
mess around with core system settings like hardware clock without
confusing any apps that are running. I mean rebooting the OS, not
restarting the process

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