On Wed, Aug 18, 2021 at 11:15 AM Parav Pandit <parav@xxxxxxxxxx> wrote: > > > > > From: Michael S. Tsirkin <mst@xxxxxxxxxx> > > Sent: Tuesday, August 17, 2021 2:24 AM > > > > On Mon, Aug 09, 2021 at 09:51:49AM +0000, Parav Pandit wrote: > > > > From: Michael S. Tsirkin <mst@xxxxxxxxxx> > > > > Sent: Monday, August 9, 2021 3:10 PM > > > > > > > > On Fri, Aug 06, 2021 at 08:55:56AM +0000, Parav Pandit wrote: > > > > > > > > > > > > > > > > > > > > > > The point is to try and not reinvent a dedicated vpda interface > > > > > > where a generic one exits. > > > > > > E.g. for phy things such as mac speed etc, I think most people > > > > > > are using ethtool things right? > > > > > > > > > > As you know vdpa is the backend device for the front-end netdevice > > > > accessed by the ethtool. > > > > > vdpa management tool here is composing the vdpa device. > > > > > > > > > > For example creator (hypervisor) of the vdpa devices knows that a > > > > > guest VM is given 4 vcpus, So hypervisor creates a vdpa devices > > > > > with config space layout as, max_virtqueue_pairs = 4. > > > > > And the MAC address chosen by hypervisor in mac[6]. > > > > > > > > > > Guest VM ethtool can still chose to use less number of channels. > > > > > > > > > > Typically, > > > > > ethtool is for guest VM. > > > > > vdpa device is in hypevisor. > > > > > > > > > > How can hypervisor compose a vdpa device without any tool? > > > > > How can it tell ethtool, what is supported and what are the defaults? > > > > > > > > > > I must be misunderstanding your comment about ethtool. > > > > > Can you please explain? > > > > > > > > > > > > I am basically saying that we probably want to be able to change MAC > > > > of a VDPA device on the host without desroying and recreating the > > > > device as long as it's not in use. > > > Ok. I understood your comment now. > > > Yes, this was the objective which is why they are present as independent > > config knob. > > > Jason was suggesting to have them as creation only knobs, which requires > > recreate. > > > > > > I don't have strong opinion for either method. > > > > > > Passing them at creation time is simpler for user. > > > If user needs the ability to modify and reuse same device with different > > config, extending such support in future like this patch should possible. > > > > > > So there are two questions to close. > > > 1. Can we start with config params at vdpa device creation time? > > > > I'm not sure whether we need both but I'd like to see a full API and I think we > > all agree host wants ability to tweak mac after device creation even if guest is > > not allowed to change mac, right? > > > Yes. > $ vdpa dev add name foo mgmtdev pci/0000:03:00.0 mac 00:11:22:33:44:55 maxvqs 8 mtu 9000 > > Above API if we do at creation time. It is likely simpler for user to pass necessary params during creation time. > > > > 2. Is it ok to have these config params as individual fields at netlink U->K > > UAPI level? > > > This is the method proposed in this patch series. > > > (Similar to incrementally growing vxlan ip link command). > > > > > > Or > > > They should be packed in a structure between U-> K and deal with > > typecasting based on size and more? > > > (Jason's input). > > > > I'm inclined to say vxlan is closer to a model to follow. > Ok. thanks for the feedback. We are using the model close to vxlan. > Lets resolve should we have it at creation time, post creation or both? > (a) Creation time > Pros: > - simpler single api for user > - eliminates needs of inventing stats reset in future series > Cons: > - inability to reuse the device with different config This can be solved by destroying the instance and re-creating it with a different params? > - This may not be of great advantage, and it is probably fine to have creation time params > > (b) post creation time: > Pros: > - able to reuse the device with different config for say different VM. > - will require stats reset in future once stats are implemented Any reason for doing this other than re-creating the device? > Cons: > - more commands for users to config a device, better to have the ability at create time. We probably need to support post creation but it should be device specific. E.g we may support device resize for virtio-blk devices. But it can be done on top I think. Thanks > > > > > -- > > MST > _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
