On Thu, Mar 13, 2014 at 05:26:05AM -0600, Eric Blake wrote:
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.
We've got docs about the various policies already, in that link above. What's missing is explanation of thee <catchup> sub-element attributes. These were added in commit 4ee2b31804f4d3477ee83bac28d9991afb0c3393 Author: Laine Stump <laine@laine.org> Date: Wed Mar 31 13:03:54 2010 -0400 Changes to clock timer XML to match final design. The clock timer XML is being updated in the following ways (based on further off-list discussion that was missed during the initial implementation): 1) 'wallclock' is changed to 'track', and the possible values are 'boot' (corresponds to old 'host'), 'guest', and 'wall'. 2) 'mode' has an additional value 'smpsafe' 3) when tickpolicy='catchup', there can be an optional sub-element of timer called 'catchup': <catchup threshold=123 slew=120 limit=10000/> Those three values are all longs, always optional, and if they are present, they are positive. Internally, 0 indicates "unspecified". Even more strangely AFAICT, nothing in any libvirt driver ever uses the threshold/slew/limit values, so I'm wondering why we added them to the XML.... Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|