On 2/1/23 12:19, Eugenio Perez Martin wrote:
On Wed, Feb 1, 2023 at 12:14 PM Maxime Coquelin
<maxime.coque...@redhat.com> 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.
Can you expand on this? I think my proposal does not require modifying
anything in the device. Or you mean hw/virtio/vhost-user.c and
similar?
I had deeper look, and both proposals should not be very different in
term of rework on DPDK side.
Maxime
Thanks!
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.
Sure, that would be great.
Thanks!
