On 10/03/2012 04:08 PM, Ben Clay wrote: > I'm trying to track balloon growth after issuing a setmem command to a KVM > guest with libvirt 0.10.2 and qemu-kvm 0.12.1.2 on CentOS 6.3. libvirt > 0.10.2 was built from tar today and appears to be working fine. The guest > is running CentOS 6.3 as well. > > Is my understanding incorrect of what VIR_DOMAIN_EVENT_ID_BALLOON_CHANGE is? This event is only fired if you have qemu 1.2 or newer, or if the new BALLOON_CHANGE event has been backported to the particular qemu you are using. > Is there something else this event is tracking, other than a virsh -c > qemu:///system setmem <dom> <mem in KB> command and/or subsequent balloon > movement inside the guest? The event is currently tracking when qemu events occur. > Or, is my old version of qemu-kvm not passing > this event back to libvirt? Correct. > The latter doesn't seem correct because I'm > getting seemingly-valid values from dommemstat - ie, if I setmem 200MB when > the guest OS and applications are consuming 300MB, it reports near 300MB > (and the guest no longer responds) instead of just parroting the 200MB value > I fed it. You are seeing different values because libvirt is doing polling under the hood, when talking to a qemu too old to send the event. If you upgrade qemu to something that sends the JSON event, then libvirt will quit polling, and instead rely on the event and forward the event back to you. We could argue that since libvirt is already polling older qemu, that libvirt should then synthesize VIR_DOMAIN_EVENT_ID_BALLOON_CHANGE any time it happens to detect a change on one of its polls, but I'm not sure if it is easier to write that patch than it is to just tell people to upgrade to newer qemu. Besides, with libvirt polling, the events will only happen insofar as libvirt detects change, which might be at a different frequency than how newer qemu would fire the events (note that the qemu 1.2 implementation rate-limits the event, to fire at most once per second, with the last event firing as late as 1 second after the actual final change of the memory). That is, synthesizing the event in libvirt for older qemu would require implementing the same rate-limiting code in libvirt. Since you mentioned are using CentOS, you are at the mercy of what others happen to package; if this feature is really important to you, you might want to consider contributing patches upstream, and/or switching to a RHEL contract to get Red Hat to implement it faster on your behalf. -- Eric Blake eblake@xxxxxxxxxx +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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