On Wed, Feb 01, 2023 at 12:14:18PM +0100, Maxime Coquelin wrote: > Thanks Eugenio for working on this. > > On 1/31/23 20:10, Eugenio Perez Martin wrote: > > Hi, > > > > The current approach of offering an emulated CVQ to the guest and map > > the commands to vhost-user is not scaling well: > > * Some devices already offer it, so the transformation is redundant. > > * There is no support for commands with variable length (RSS?) > > > > We can solve both of them by offering it through vhost-user the same > > way as vhost-vdpa do. With this approach qemu needs to track the > > commands, for similar reasons as vhost-vdpa: qemu needs to track the > > device status for live migration. vhost-user should use the same SVQ > > code for this, so we avoid duplications. > > > > One of the challenges here is to know what virtqueue to shadow / > > isolate. The vhost-user device may not have the same queues as the > > device frontend: > > * The first depends on the actual vhost-user device, and qemu fetches > > it with VHOST_USER_GET_QUEUE_NUM at the moment. > > * The qemu device frontend's is set by netdev queues= cmdline parameter in > > qemu > > > > For the device, the CVQ is the last one it offers, but for the guest > > it is the last one offered in config space. > > > > To create a new vhost-user command to decrease that maximum number of > > queues may be an option. But we can do it without adding more > > commands, remapping the CVQ index at virtqueue setup. I think it > > should be doable using (struct vhost_dev).vq_index and maybe a few > > adjustments here and there. > > > > Thoughts? > > I am fine with both proposals. > I think index remapping will require a bit more rework in the DPDK > Vhost-user library, but nothing insurmountable. > > I am currently working on a PoC adding support for VDUSE in the DPDK > Vhost library, and recently added control queue support. We can reuse it > if we want to prototype your proposal. > > Maxime > > > Thanks! > >
technically backend knows how many vqs are there, last one is cvq... not sure we need full blown remapping ... -- MST
