Re: [Xen-devel] [PATCH 0/3] xen: fix various wallclock problems

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 12/10/12 13:57, David Vrabel wrote:
> This series (with some toolstack updates) corrects a number of cases
> where a guest can see an incorrect wallclock time.
> 
> 1. Systems with NTP won't periodically synchronize the hardware RTC so
> the wallclock may be incorrect after a reboot.
> 
> 2. The wallclock is always ~500 ms behind the correct time.
> 
> 3. If the system time was stepped and NTP isn't synchronized yet, the
> wallclock will still have the incorrect time.  The fix for this
> requires the toolstack to synchronize the wallclock -- patch #3
> provides the mechanism for this.

These tables should help.

Before:

              |                Updates
Process       | System Time?  Xen Wallclock?  Hardware Clock?
-------------------------------------------------------------
date -s       | X
hwclock -w    |                               X
ntpd          | X             X[*]
ntpdate       | X

After this (and the toolstack) patches:

              |                Updates
Process       | System Time?  Xen Wallclock?  Hardware Clock?
-------------------------------------------------------------
date -s       | X
hwclock -w    |                               X
ntpd          | X             X[*]            X[*]
ntpdate       | X
xen-wallclock |               X

[*] every 11 minutes.

David

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