[Kimchi-devel] [RFC] Guest/Template CPU setup with topology

[Daniel Henrique Barboza]

On 11/10/2016 11:12 AM, Chandra Shekhar Reddy Potula wrote:
>
>
> On 11/9/16 12:44 AM, Daniel Henrique Barboza wrote:
>> Hi there,
>>
>> At this moment Kimchi support for guest and template CPU setup is
>> underwhelming. Here's what I've found that needs improving:
>>
>> - edit template:
>>
>> * calculation of max CPUs is wrong when considering a topology. Max CPU
>> is the value of sockets * cores *  threads. At this moment it is 
>> considering only
>> cores * threads, defaulting sockets to 1.
>>
>> * There is no way to set or even see the value of sockets. Given that 
>> this value
>> is used in the calculation of the max CPUs, it should be at least 
>> visible and, in my
>> opinion, editable
>>
>>
> I like the idea. One thing to consider here is these calculations 
> might be different based on platforms (x86/ppc/s390x). Make sure we 
> have to address these aspects.

The calculation is the same for Intel and Power archs.  I am assuming that
it is the same for s390x. If it's not we can make exceptions in this case.

>> - edit guest (not running):
>> * If the guest was created with a CPU topology, there is no way to 
>> edit it. The only
>> way to edit a topology at this moment is on the template level.
>>
>>
>> My proposal is:
>>
>> edit template:
>> - fix the max CPU calculation to consider the sockets.
>> - add a field to allow the 'sockets' to be set at will. Default value 
>> will be retrieved
>> by the kimchi/host/cpuinfo API as a reference (same think as with 
>> cores and threads
>> today).
>>
>> edit guest:
>> - if the guest was created with a CPU topology, allow the topology to 
>> be edited when
>> the guest is turned OFF.
>>
>>
>> Thoughts?
>>
>>
> Looks good
>>
>> ps: this RFC is also related to the feedback of "Bug fix #1072 - 
>> changing vpus
>> verification​".
>>
> Also in any means max number of vcpu that can be created based on the 
> CPU capacity available to the host to be addressed ? May be this is 
> some thing we can attempt if it helps admin. Just a thought !!!

The limitation is given by libvirt. Not sure if it takes the host 
capabilities
into account. This laptop I use has 4 CPUs but libvirt allows me to
create KVM guests with far more CPU than that:


[danielhb at arthas ginger]$ sudo python
Python 2.7.12 (default, Sep 29 2016, 13:30:34)
[GCC 6.2.1 20160916 (Red Hat 6.2.1-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> import libvirt
 >>> conn = libvirt.open('qemu:///system')
 >>> conn.getMaxVcpus('kvm')
288


So, for my current setup, I can have a KVM guest with up to 288
CPUs (of course that the host performance will go to drain if I
do that hehehe).


Daniel


>>
>> Daniel
>>
>>
> +1 for the proposal
>>
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