Re: [Libvir] "virsh list" command of libvirt consumes a lot of CPU in the domain-0
On Tue, Mar 11, 2008 at 04:48:57PM +0100, jean-paul.pigache(a)bull.net wrote:
Hi all,
I know that this is not a libvirt issue but this badly impacts libvirt
usage.
Is anyone aware of any status on this issue ? Daniel ?
Here is some history I could get from the libvirt mailing list :
* October 12, 2006 (Daniel Berrange).
I've been trying to track down just why talking to XenD is resulting
in so much CPU time being
comsumed by both xend & xenstored. As a test case, I'm running 'virsh
dominfo demo' which results in
a single HTTP request to Xend to fetch domain info, eg 'GET
/xend/domains/demo'
Run this in a tight loop & I'll see xenstored taking > 50% CPU, and
XenD taking another 11%
yes this is a serious performance issue in xend.
[...]
single read in XenD. Now if I
monitor the status of 20 domains, once per second that's causing 40 MB
of writes & 40 MB of reads
every second which is utterly ridiculous & completely non scalable for
enterprise deployment :-(
agreed
[...]
> Xen 3.0.3 has a serious performance bug
> (see
http://lists.xensource.com/archives/html/xen-devel/2006-10/msg00487.ht
ml)
> This bug is fixed in Xen 3.0.4
No it isn't. The performance bug is actually at least x2 worse in Xen
3.0.4
I was told that xenstored had been rewritten for the Xen Enterprise version.
There is little I can do at that level honnestly, in libvirt we need the
xend access only to make the binding between the domain ID and the domain
name. All update informations are provided by the hypervisor, including
the ID list, something we could do is to try to cache the id <-> name
domain association, this is a bit risky since there is no way libvirt can
learn that a binding has changed (either because of an xm rename command
or the domain was destroyed and a new domain created with same id).
If we keep the association in the daemon and use a timeout flush maybe
this could be worked out, but it's really a bad workaround, and the
proper thing would be to fix this long standing bug in xenstored, it's a bit
depressing that no progress had been made on the open source version.
Daniel
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