On Mon, Jan 20, 2020 at 09:47:18PM +0000, Shahaf Shuler wrote: > Monday, January 20, 2020 11:25 PM, Michael S. Tsirkin: > > Subject: Re: [PATCH 3/5] vDPA: introduce vDPA bus > > > > 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... > > The fact memory hotplug is enabled doesn't necessarily means there is not cold-plugged memory on the hot plugged slots. > So your claim is majority of guests are deployed w/o any cold-plugged memory? Sorry for not being clear. I was merely saying that dynamic one can't be optional, and static one can. So how about we start just with the dynamic one, then add the static one as a later optimization? > > > > > > > > > > > > If the first one, then I think memory hotplug is a heavy flow > > > > > > regardless. Do you think the extra cycles for the tree traverse > > > > > > will be visible in any way? > > > > > > > > > > I think if the driver can pause the DMA during the time for > > > > > setting up new mapping, it should be fine. > > > > > > > > This is very tricky for any driver if the mapping change hits the > > > > virtio rings. :( > > > > > > > > Even a IOMMU using driver is going to have problems with that.. > > > > > > > > Jason
