RE: [Libvirt] Attach qemu commands to an running xml domain
-----Original Message-----
From: Michal Privoznik <mprivozn(a)redhat.com>
Sent: Wednesday, March 31, 2021 5:49 PM
To: Moshe Levi <moshele(a)nvidia.com>; Daniel P. Berrangé
<berrange(a)redhat.com>
Cc: Waleed Musa <waleedm(a)nvidia.com>; libvir-list(a)redhat.com; Adrian
Chiris <adrianc(a)nvidia.com>
Subject: Re: [Libvirt] Attach qemu commands to an running xml domain
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On 3/31/21 4:01 PM, Moshe Levi wrote:
>
>
>> -----Original Message-----
>> From: Daniel P. Berrangé <berrange(a)redhat.com>
>> Sent: Wednesday, March 31, 2021 3:23 PM
>> To: Michal Privoznik <mprivozn(a)redhat.com>
>> Cc: Waleed Musa <waleedm(a)nvidia.com>; libvir-list(a)redhat.com;
Moshe
>> Levi <moshele(a)nvidia.com>; Adrian Chiris <adrianc(a)nvidia.com>
>> Subject: Re: [Libvirt] Attach qemu commands to an running xml domain
>>
>> I've always thought if we wanted to support use of resources from
>> other namespaces, then that would involve use of a namespace="$PID"
>> attribute to identify the namespace.
>>
>> <source type='unix' namespace="523532"
>> path='/var/lib/vhost_sockets/sock7f9a971a-cf3'
mode='server'/>
>>
>> IOW, libvirt could enter the namespace, and then talk to the OVS
>> db.sock at its normal location.
>>
>> It would be bit strange having namespace refer to a different NS for
>> the OVS, but using the path=/var/lib/..... from the current
>> namespace, but as long as we define the semantics clearly its not the end
of the world.
> Just to better explain the use case here so we have user space vdpa
solution which requires the following qemu flags to work:
> 1. page-per-vq=on
> 2. host_mtu
>
> I understand the adding page-per-vq is feature requested to I am putting
that aside.
Correct.
>
> Regarding the host_mtu we want to use the libvirt xml to set mtu like in [1]
so we can set mtu in hot plug.
> Basically we just want that the libvirt xml mtu will just set the qemu
host_mtu.
> Th problem is the this using mtu in libvirt xml will query ovs (it assume that
if ovs installed on the host it needs to set it mtu).
> In our case we have OVS running on the host for switching and OVS in
> container to connect the VF netdevice with vhostuser to qemu to just
> forward traffic from VF to virtio using vdpa) 1. One option is to
> allow to disable the set of mtu in ovs so it will just add the qemu
> host_mtu flag (we can set the mtu on ovs by openstack)
Don't you need to set the MTU also on the TAP device? Or will it be inherited
from the OVS bridge?
In our case it MTU of the VF nerdevice and we set it by OVS.
> 2. Second option is to change how we query ovs to add --db flag so we
> can change the query to be on the ovs in the container
>
> Both option are fine with me.
>
Michal