[Libvir] [PATCH] Xen: Support cpu_weight and cpu_cap for Xen.

Daniel Veillard veillard at redhat.com
Wed Oct 24 09:46:46 UTC 2007

On Wed, Oct 24, 2007 at 04:35:33PM +0900, Tatsuro Enokura wrote:
> Hi,
> I set the information of cpu_weight/cpu_cap to configuration file or
> sxp format, and execute "virsh start".
> But the information of weight/cap is lost.
> libvirt doesn't support cpu_weight and cpu_cap for XML format.

  Right. To me cpu_weight and cpu_cap are tuning informations
they are completely dependant:
    - on the hypervisor used (only Xen)
    - on a specific scheduler for said hypervisor
    - on the runtime operations conditions, i.e. you may want to
      revise those settings if you migrate the domain, or change
      anything on the target host
 So you are suggesting to add this to the XML, while for me this makes little
sense because of all this specificity.
I have no doubt the patch would 'work' for you, but anybody using a different
hypervisor, or different scheduler, or even someone trying to understand what
those fields are would have no use or informations (your patch does not provide
documentation for the meaning of those attributes).

  I have a problem with extending the XML in a way which makes sense
only for one hypervisor, when using a specific scheduler, and without
a proper definition for what the extension actually means. 
  Also Those informations are highly runtime dependant, it's tuning,
it is not critical at all to get that tuning to get the domain up and
running, and once it is running you can actually use the libvirt API
to make the scheduler tuning.

  Can you explain why you absolutely want to have that tuning information
in the XML itself ?

> see also Bz#337591
>   https://bugzilla.redhat.com/show_bug.cgi?id=337591

  That's your request, not really a justification

> I make a patch to add weight/cap attributes as vcpus element
>   (eg. <vcpus weight='512' cap='280'>4</vcpus>)
> c.f. the thread at:
>   https://www.redhat.com/archives/libvir-list/2007-October/msg00044.html

That thread was absolutely not discussing specific Xen scheduling parameters
it was discussing how to express the set of CPUs a domain should start on
and this information is not Xen specific in nature.


Red Hat Virtualization group http://redhat.com/virtualization/
Daniel Veillard      | virtualization library  http://libvirt.org/
veillard at redhat.com  | libxml GNOME XML XSLT toolkit  http://xmlsoft.org/
http://veillard.com/ | Rpmfind RPM search engine  http://rpmfind.net/

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