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

[Michael S. Tsirkin]

On Tue, Jan 21, 2020 at 02:07:59PM +0000, Jason Gunthorpe wrote:
> 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.

Right. But let let's get basic functionality working first.

> Perhaps Shahaf can quantify the performance delta?
> 
> Jason