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



* Richard W.M. Jones <rjones redhat com> [2010-09-06 17:59]:
> On Mon, Sep 06, 2010 at 05:46:03PM +0200, Wolfram Schlich wrote:
> > * Richard W.M. Jones <rjones redhat com> [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.

xentop is *magnitudes* faster than virt-top, really.
"xm list" takes ages whereas "xenstore-list /local/domain"
is quite fast, also "xenstore-list /local/domain \
	| while read domid; do \
	xenstore-read /local/domain/${domid}/name; done"
(to get even the domain's name).

Cheers,
Wolfram


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