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

9 Jun 2018


      On Sat, Jun 09, 2018 at 03:13:56PM +0800, bing.niu 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
On 2018年06月08日 21:00, Pavel Hrdina wrote:
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.
Yes, I don't like that confusion as well.  We will see how the code will
look like and how it will behave whether it makes sense or not.  If
needed we can change it.

Pavel