[libvirt] [RFC PATCH 0/2] Introduce RDT memory bandwidth allocation support

[bing.niu]

On 2018年06月08日 21:00, Pavel Hrdina wrote:
> On Wed, Jun 06, 2018 at 03:46:37PM +0800, bing.niu wrote:
>> Hi Pavel,
>>
>> On 2018年06月06日 13:56, bing.niu wrote:
>>
>>>>
>>>> Then there is the domain XML, for CAT we use this:
>>>>
>>>> <domain>
>>>>     ...
>>>>     <cputune>
>>>>       ...
>>>>       <cachetune vcpus='0-3'>
>>>>         <cache id='0' level='3' type='both' size='3' unit='MiB'/>
>>>>         <cache id='1' level='3' type='both' size='3' unit='MiB'/>
>>>>       </cachetune>
>>>>       ...
>>>>     <cputune>
>>>>     ...
>>>> </domain>
>>>>
>>>> so the possible domain XML could look like this:
>>>>
>>>> <domain>
>>>>     ...
>>>>     <cputune>
>>>>       ...
>>>>       <memory vcpus='0-3'>
>>>>         <socket id='0' bandwidth='30'/>
>>>>         <socket id='1' bandwidth='20'/>
>>>>       </memory>
>>>>       ...
>>>>     <cputune>
>>>>     ...
>>>> </domain>
>>>>
>>>> Again, the element names 'memory' and 'socket' can be named differently.
>>> socket --> node?
>>>
>>> Since the existing virrestrl implementation only care about cache part
>>> during development, So we may need change some names of structure and
>>> functions when enable MBA. How do you think
>>>>
>>>> Pavel
>>>>
>>>
>> Is that possible to support MBA by extending CAT in domain XML? Since each
>> <cachetune> will map to one virresctrlalloc structure and create a rdt_group
>> in resctrl fs. Each rdt_group will have it's own closid. this work perfect
>> if CAT only available. However, if MBA coming in with CAT enabled also, ike
>> this.
>>
>> <domain>
>>      ...
>>      <cputune>
>>        ...
>>        <cachetune vcpus='0-3'>
>>          <cache id='0' level='3' type='both' size='3' unit='MiB'/>
>>          <cache id='1' level='3' type='both' size='3' unit='MiB'/>
>>        </cachetune>
>>       <memory vcpus='2-3'>
>>         <socket id='0' bandwidth='30'/>
>>         <socket id='1' bandwidth='20'/>
>>       </memory>
>>        ...
>>      <cputune>
>>      ...
>> </domain>
>>
>> we have to make sure those two allocating will not have vcpu overlapped.
>> like this,
>>
>> if (virBitmapOverlaps(def->cachetunes[i]->vcpus, vcpus)
>> || virBitmapOverlaps(def->memroy->vcpus, vcpus)) {
>>               virReportError(VIR_ERR_XML_ERROR, "%s",
>>                              _("Overlapping vcpus in cachetunes"));
>>               goto cleanup;
>> that looks like introducing some dependency between CAT and MBA.
>> Is that possible we rename cachetune so that handle CAT MBA together one
>> section?
> 
> I would like to avoid mixing cache tune and memory bandwidth under
> 'cachetune' element.  But this is a good point, we need to make sure
> that the 'vcpus' is not overlapping.
> 
> Renaming existing XML element is not possible, it needs to be backward
> compatible.
> 
> Pavel
thanks for clarification ；）. we will do a cross check about cachetune 
and memory to make sure no vcpus overlapping. I just feel this may 
confuse people. Since we must tell them vcpus cannot overlapping for 
cachetune and memory, but vcpus can be equal. this should be the most 
common case--- create one rdt group for one vm.



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