On Thu, Jun 20, 2024 at 05:38:22PM +0800, Heng Qi wrote:
> On Thu, 20 Jun 2024 04:32:15 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > On Thu, Jun 20, 2024 at 03:29:15PM +0800, Heng Qi wrote:
> > > On Wed, 19 Jun 2024 17:19:12 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > > On Thu, Jun 20, 2024 at 12:19:05AM +0800, Heng Qi wrote:
> > > > > @@ -5312,7 +5315,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> > > > >
> > > > > /* Parameters for control virtqueue, if any */
> > > > > if (vi->has_cvq) {
> > > > > - callbacks[total_vqs - 1] = NULL;
> > > > > + callbacks[total_vqs - 1] = virtnet_cvq_done;
> > > > > names[total_vqs - 1] = "control";
> > > > > }
> > > > >
> > > >
> > > > If the # of MSIX vectors is exactly for data path VQs,
> > > > this will cause irq sharing between VQs which will degrade
> > > > performance significantly.
> > > >
> > > > So no, you can not just do it unconditionally.
> > > >
> > > > The correct fix probably requires virtio core/API extensions.
> > >
> > > If the introduction of cvq irq causes interrupts to become shared, then
> > > ctrlq need to fall back to polling mode and keep the status quo.
> > >
> > > Thanks.
> >
> > I don't see that in the code.
> >
> > I guess we'll need more info in find vqs about what can and what can't share irqs?
>
> I mean we should add fallback code, for example if allocating interrupt for ctrlq
> fails, we should clear the callback of ctrlq.
I have no idea how you plan to do that. interrupts are allocated in
virtio core, callbacks enabled in drivers.
> > Sharing between ctrl vq and config irq can also be an option.
> >
>
> Not sure if this violates the spec. In the spec, used buffer notification and
> configuration change notification are clearly defined - ctrlq is a virtqueue
> and used buffer notification should be used.
>
> Thanks.
It is up to driver to choose which msix vector will trigger.
Nothing says same vector can't be reused.
Whether devices made assumptions based on current driver
behaviour is another matter.
> >
> >
> >
> > > >
> > > > --
> > > > MST
> > > >
> >
> >
