Re: [PATCH 3/5] vDPA: introduce vDPA bus

Jason Gunthorpe
2020-01-21T14:08:10Z

On Mon, Jan 20, 2020 at 04:25:23PM -0500, Michael S. Tsirkin wrote:
> On Mon, Jan 20, 2020 at 08:51:43PM +0000, Shahaf Shuler wrote:
> > Monday, January 20, 2020 7:50 PM, Jason Gunthorpe:
> > > Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus
> > >
> > > On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote:
> > > > This is similar to the design of platform IOMMU part of vhost-vdpa. We
> > > > decide to send diffs to platform IOMMU there. If it's ok to do that in
> > > > driver, we can replace set_map with incremental API like map()/unmap().
> > > >
> > > > Then driver need to maintain rbtree itself.
> > >
> > > I think we really need to see two modes, one where there is a fixed
> > > translation without dynamic vIOMMU driven changes and one that supports
> > > vIOMMU.
> > >
> > > There are different optimization goals in the drivers for these two
> > > configurations.
> >
> > +1.
> > It will be best to have one API for static config (i.e. mapping can be
> > set only before virtio device gets active), and one API for dynamic
> > changes that can be set after the virtio device is active.
>
> Frankly I don't see when we'd use the static one.
> Memory hotplug is enabled for most guests...

If someone wants to run a full performance application, like dpdk,
then they may wish to trade memory hotplug in that VM for more
performance.

Perhaps Shahaf can quantify the performance delta?

Jason