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Re: [Xen-devel] "right" way to gather domU stats in xen 3 & 4?

To: Florian Heigl <florian.heigl@xxxxxxxxx>
Subject: Re: [Xen-devel] "right" way to gather domU stats in xen 3 & 4?
From: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date: Tue, 1 Mar 2011 11:13:01 +0000
Cc: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>
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On Mon, 28 Feb 2011, Florian Heigl wrote:
> Any comment about tmem / baloon would still be great... why doesn't
> anyone jump when our coolest features are mentioned? :)
> I think it's important to make them visible to the general users...

Ballooning shouldn't be difficult, it is just a matter of reading
memory/target and memory/static-max from xenstore.
You could also read the actual memory used by the domain and compare it
with target.
Regarding tmem I'll let Dan comment on it.

> >> That's just a 1.5GHz VIA box, but I'll have to see how long it takes
> >> for 100 VMs or more.
> >
> > Xenstore can become very busy on systems with many VMs running.
> So, any advice? Obviously, limiting my queries is the main trick, but
> seems the tools do a lot of calls internally.
> I wonder if that post about xenstore IO performance
> http://xen.1045712.n5.nabble.com/Revisiting-XenD-XenStored-performance-scalability-issues-td2504870.html
> still applies. I'll try the ramdisk hack he described out of
> curiosity.

It still applies to XenD but nowadays the development is mostly on
xl/libxenlight that in response to "xl list" does a xenstore read per
domain to resolve the domain name.
If you are not interested in the domain name you could just call
libxl_list_domain to have the list of domains running with a basic set
of information (see libxl_dominfo, contains memory usage, cpu usage and
number of online vcpus), no xenstore transactions at all!

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