Re: [Virtio-fs] [PATCH v3 07/20] virtio: add vhost-user-base and a generic vhost-user-device

[Matias Ezequiel Vara Larsen <mvaralar@redhat.com>]

On Tue, Sep 05, 2023 at 06:01:56PM +0100, Alex Bennée wrote:
> 
> Matias Ezequiel Vara Larsen <mvaralar@redhat.com> writes:
> 
> > On Mon, Jul 10, 2023 at 04:35:09PM +0100, Alex Bennée wrote:
> >> In theory we shouldn't need to repeat so much boilerplate to support
> >> vhost-user backends. This provides a generic vhost-user-base QOM
> >> object and a derived vhost-user-device for which the user needs to
> >> provide the few bits of information that aren't currently provided by
> >> the vhost-user protocol. This should provide a baseline implementation
> >> from which the other vhost-user stub can specialise.
> >> 
> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> >> 
> >> ---
> >> v2
> >>   - split into vub and vud
> <snip>
> >> +
> >> +    /*
> >> +     * Disable guest notifiers, by default all notifications will be via the
> >> +     * asynchronous vhost-user socket.
> >> +     */
> >> +    vdev->use_guest_notifier_mask = false;
> >> +
> >> +    /* Allocate queues */
> >> +    vub->vqs = g_ptr_array_sized_new(vub->num_vqs);
> >> +    for (int i = 0; i < vub->num_vqs; i++) {
> >> +        g_ptr_array_add(vub->vqs,
> >> +                        virtio_add_queue(vdev, 4, vub_handle_output));
> >> +    }
> >> +
> >
> > Hello Alex, apologies if someone already asked this. If I understand
> > correctly, the second parameter of virtio_add_queue() is the len of the
> > queue. Why have you chosen "4" as its value? Shall qemu query the len of
> > the queue from the vhost-user device instead?
> 
> Hmm yeah that is inherited from the virtio-rng backend which has a
> pretty short queue. I don't think it is intrinsic to the device
> implementation (although I guess that depends if a device will have
> multiple requests in flight).
> 
> I propose making is some useful ^2 (like 64) and adding a config knob to
> increase it if needed.
> 

LGTM.  

Matias