Re: [libvirt] virt-top version bump in EPEL5

On Mon, Sep 06, 2010 at 04:58:42PM +0100, Richard W.M. Jones wrote: > On Mon, Sep 06, 2010 at 05:46:03PM +0200, Wolfram Schlich wrote: > > * Richard W.M. Jones <rjones(a)redhat.com&gt; [2010-09-06 17:23]: > > > On Mon, Sep 06, 2010 at 05:06:55PM +0200, Wolfram Schlich wrote: > > > > We are experiencing a problem with virt-top on our RHEL5 virthosts. > > > > > > > > On a heavily loaded virthost, virt-top is damn slow -- it takes 4-5s > > > > to update and imposes a noticeable load on the dom0 as well > > > > (xenstored shows up in top eating all CPU for some seconds). > > > > xentop seems to impose *much* less load on the dom0. > > > > Is there something I can do about it? > > > > > > > > Another problem: 0.3.3.1 shows RDRQ/WRRQ/RXBY/TXBY after some seconds > > > > whereas 1.0.4 does not...? > > > > > > I bet both of these will be libvirt issues. > > > > > > Try running: > > > > > > virsh list --all > > > > Takes around 2-4s depending on dom0 load. > > CC-ing to libvir-list. There may be a better way now for virt-top to > get the list of domains, but if 'virsh list --all' is also slow, then > it's probably a generic libvirt problem. > > > > virsh domblkstat DomainName hda > > > > s/hda/xvda/ I guess :) > > This one is quite fast, below 0.2s. > > > > > virsh domifstat DomainName vnet0 > > > > This takes around 0.1s most of the time, but sometimes around 1.0s. > > > > > etc. > > > > > > If those commands (done in a suitable loop) also cause load on the > > > dom0, and if domblkstat/domifstat don't show stats, then it's down to > > > libvirt. > > > > > > virt-top is a simple little program that just exercises those libvirt > > > APIs ... > > > > Hmm :/ So I guess we're better off with xentop... > > We should be able to have performance very close to xentop. After > all, libvirt makes exactly the same direct hypervisor calls. It depends on which API calls virt-top makes. The virConnectListDomains goes to XenStore (fast), virDomainLookupByID/UUID go to HV (fast). The possibly bad ones are virConnectDefinedDomains goes to /etc/xen (fast) or XenD (slow) and virDomainLookupByName goes to XenD (slow). virsh list --all is slow because inactive domains requires using those latter two APIs which hit XenD. virt-top/xentop shouldn't care about inactive domains though, since they've obviously no interesting CPU time to report :-)

In a perfect world you'd also want to use the lifecycle events, so you only need call ListDomains/ListDefinedDomains once, and then get explicit notifications of new virDomainPtr instances without any need todo a lookup.