Re: virtio performance analysis

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 14, 2013 at 11:37:35AM +0530, nitesh narayan lal wrote:
> I was wondering how exactly vq->event is been set and used?
> Regards
> Nitesh Narayan Lal
> 
> 
> On Tue, May 14, 2013 at 11:37 AM, nitesh narayan lal
> <niteshnarayanlalleo@gmail.com> wrote:
> > Hi Michael,
> > I had seen the virtqueue_kick_prepare() where vring_need_event() is
> > been used, but somehow for every start_xmit() call vq->event and
> > need_kick is been set to true.
> > Due to which for every start_xmit() its kicking via notify() routine.
> > Regards
> > Nitesh Narayan Lal


vq->event if set when guest and host agree to use event index.
needs_kick comes from comparison of event index (element for
which host requested an event) and avail index.

We trigger the event when we make available the element
for which host requested notification.

More detail in the virtio spec.

-- 
MST