Re: [PATCH RFC v2 0/3] vdpa: dedicated descriptor table group

[Jason Wang <jasowang@redhat.com>]

On Mon, Sep 11, 2023 at 3:06 PM Dragos Tatulea <dtatulea@nvidia.com> wrote:
>
> Hi Jason,
>
> On Mon, 2023-09-11 at 14:43 +0800, Jason Wang wrote:
> > On Sat, Sep 9, 2023 at 4:45 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
> > >
> > > Following patchset introduces dedicated group for descriptor table to
> > > reduce live migration downtime when passthrough VQ is being switched
> > > to shadow VQ. This RFC v2 is sent to incorporate the early feedback
> > > from reviewers on the uAPI and driver API part of changes, the
> > > associated driver patch set consuming ths API will come around
> > > soon along with formal submission of this series.
> > >
> > > Some initial performance data will be gathered using the real
> > > hardware device with mlx5_vdpa. The target goal of this series is to
> > > reduce the SVQ switching overhead to less than 300ms on a ~100GB
> > > guest with 2 non-mq vhost-vdpa devices. The reduction in the downtime
> > > is thanks to avoiding the full remap in the switching.
> > >
> > > The plan of the intended driver implementation is to use a dedicated
> > > group (specifically, 2 in below table) to host the descriptor tables
> > > for data vqs, different from where buffer addresses are contained (in
> > > group 0 as below). cvq does not have to allocate dedicated group for
> > > descriptor table, so its buffers and descriptor table would always
> > > belong to the same group (1 in table below).
> > >
> > >
> > >               |  data vq | ctrl vq
> > > ==============+==========+===========
> > > vq_group      |    0     |    1
> > > vq_desc_group |    2     |    1
> > >
> > >
> > > ---
> > >
> > > Si-Wei Liu (3):
> > >   vdpa: introduce dedicated descriptor group for virtqueue
> > >   vhost-vdpa: introduce descriptor group backend feature
> > >   vhost-vdpa: uAPI to get dedicated descriptor group id
> >
> > Looks good to me but I'd expect example implementations in the parent.
> >
> We (Si-Wei and I) will send a non-RFC series with the mlx5_vdpa implementation
> as soon as the submission window opens.
>
> Can we add your Acked-by for these core patches?

Yes.

Thanks

>
> Thanks,
> Dragos

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