[libvirt-users] questions on clock catchup

[Eric Blake]

On 03/13/2014 12:49 AM, Jincheng Miao wrote:
> In http://libvirt.org/formatdomain.html#elementsTime , we could find there are
> three attributes of catchup tickpolicy: limit, threshold and slew.
> 
> "
> The catchup element has three optional attributes, each a positive integer.
> The attributes are threshold, slew, and limit.
> "
> The xml format likes:
>   <clock offset='utc'>
>     <timer name='rtc' tickpolicy='catchup'>
>       <catchup slew='123'/> or <catchup threshold='123'/> or <catchup limit='123'/>
>     </timer>
>   </clock>
> 
> But there is no further explanation.
> Does anyone know what's the meaning of these attributes ?

We ought to copy the documentation that qemu just added:

# Policy for handling lost ticks in timer devices.
#
# @discard: throw away the missed tick(s) and continue with future injection
#           normally.  Guest time may be delayed, unless the OS has explicit
#           handling of lost ticks
#
# @delay: continue to deliver ticks at the normal rate.  Guest time will be
#         delayed due to the late tick
#
# @merge: merge the missed tick(s) into one tick and inject.  Guest time
#         may be delayed, depending on how the OS reacts to the merging
#         of ticks
#
# @slew: deliver ticks at a higher rate to catch up with the missed
tick. The
#        guest time should not be delayed once catchup is complete.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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