[Libvir] RFC: requesting APIs for host physical resource discovery

[Daniel P. Berrange]

On Thu, Mar 23, 2006 at 12:35:12PM -0800, Gareth S Bestor wrote:
> I agree to some extent, but I might suggest that discovery and exposure of
> host system physical resources may be better left to other APIs, since such
> functionality has widespread uses outside of virtualization management.
> 
> Since you bring it up, we - Open Source CIM interfaces for Xen, via libvirt
> - are actually having to face this exact problem today, namely what is/are
> good standardized cross-platform cross-distro Linux interfaces for exposing
> physical hardware info necessary for virtual resource allocation. Right now
> we have a some Open Source Linux CIM providers exposing h/w info mined out
> of, say, /proc, but the architecture and distro ifdefs are getting out of
> hand... You are quite correct in stating this requirement, and there seems
> to be multiple candidates (SMBIOS, HPI, SNMP, etc) but I don't have a good
> answer. My concern would be trying to add and solve this problem within the
> scope of libvirt.

I don't think it is neccessary (or desirable) to solve the general resource 
discovery problem within libvirt - I'd limit scope to only those resources 
where there is a need for consistency with the VMM's view of resources.

Taking CPU enumeration as an example, if an app is to later instruct a VMM to
restrict scheduling of a domain's VCPUs to a particular set of host CPUs, then
it is critical to ensure the app's enumeration of host CPUs matches the way the
VMM enumerates them. eg CPU #1 in the VMM's world view, may appear as CPU #3
in /proc/cpuinfo. The most reliable way to avoid this & guarentee consistency
of view would be to have the app use the VMM for enumerating the CPUs.

Now while the app could talk to the VMM directly, it then looses the two key
benefits of libvirt - isolation from VMM comms protocol change & isolation 
from underlying virtualization technology. Thus I think libvirt needs at least
some limited resource discovery capabilities.

Regards,
Dan.
 
> |---------+------------------------------>
> |         |           "Daniel P.         |
> |         |           Berrange"          |
> |         |           <berrange at redhat.co|
> |         |           m>                 |
> |         |           Sent by:           |
> |         |           libvir-list-bounces|
> |         |           @redhat.com        |
> |         |                              |
> |         |                              |
> |         |           03/23/06 08:04 AM  |
> |         |           Please respond to  |
> |         |           "Daniel P.         |
> |         |           Berrange"          |
> |---------+------------------------------>
>   >--------------------------------------------------------------------------------------------------------------------|
>   |                                                                                                                    |
>   |       To:       libvir-list at redhat.com                                                                             |
>   |       cc:                                                                                                          |
>   |       Subject:  [Libvir] RFC: requesting APIs for host physical resource discovery                                 |
>   >--------------------------------------------------------------------------------------------------------------------|
> 
> 
> 
> 
> The current libvirt APIs allow the host's physical resources to be split up
> and allocated to guest domains, however, there is no way to discover what
> the available host resources actually are. Thus I would like to suggest the
> inclusion of new APIs to enable host resource discovery. As a starting
> point
> I'd like to be able to query the following information:
> 
>   * Number of physical CPUs - ability to enumerate the CPUs in the host,
>     both those currently present, and theoretical maximum (to take account
>     of hotplug).
>   * Amount of RAM  - actual physical RAM present, and that available for
>     guest usage (eg discounting that reserved by a hypervisor or equiv)
>   * CPU relationship - ie ability to distinguish between CPUs which
>     are hyperthread siblings, on same core, or on separate sockets
> 
> Alonside these basic queries it would be desirable to add a further
> resource
> resource management API to allow for setting of a guest domain's CPU
> affinity.
> ie ability control what CPUs the VMM is allowed to schedule a domain on.
> 
> Once this first basic set of caapbilties for resource discovery are
> provided
> for, then I believe it will be neccessary to provide some more advanced
> queries, in particular:
> 
>   * NUMA topology - ability to enumerate NUMA nodes, the CPUs associated
>     with each node & the RAM range mapped to that node
> 
> Regards,
> Dan.
> --
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-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
|=-           Perl modules: http://search.cpan.org/~danberr/              -=|
|=-               Projects: http://freshmeat.net/~danielpb/               -=|
|=-  GnuPG: 7D3B9505   F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505  -=|