[dpdk-dev] [PATCH] vhost: fix interrupt suppression for the split ring

[Tiwei Bie]

On Wed, Feb 27, 2019 at 01:38:28PM +0800, Hu, Jiayu wrote:
> > -----Original Message-----
> > From: Bie, Tiwei
> > Sent: Monday, February 25, 2019 3:07 PM
> > To: Hu, Jiayu <jiayu.hu at intel.com>
> > Cc: dev at dpdk.org; maxime.coquelin at redhat.com; stable at dpdk.org
> > Subject: Re: [PATCH] vhost: fix interrupt suppression for the split ring
> > 
> > On Fri, Feb 22, 2019 at 04:13:50PM +0800, Jiayu Hu wrote:
> > > The VIRTIO_RING_F_EVENT_IDX feature of split ring might
> > > be broken, as the value of signalled_used is unpredictable
> > > after live migration or start up. This patch fixes it by
> > > using signalled_used_valid.
> > 
> > Seems you also need to invalidate the signalled_used in e.g.
> > set_vring_base, as signalled_used may not match last_used_idx
> > anymore e.g. when guest driver is reloaded.
> 
> To handle the virtio device reload case, how about setting
> signalled_used_valid to false in get_vring_base()?

Sounds good.

> 
> Thanks,
> Jiayu
> 
> > 
> > >
> > > In addition, this patch makes the VIRTIO_RING_F_EVENT_IDX
> > > implementation of split ring match kernel backend to suppress
> > > more interrupts.
> > >
> > > Fixes: e37ff954405a ("vhost: support virtqueue interrupt/notification
> > suppression")
> > > Cc: stable at dpdk.org
> > >
> > > Signed-off-by: Jiayu Hu <jiayu.hu at intel.com>
> > > ---
> > >  lib/librte_vhost/vhost.h | 12 ++++++++----
> > >  1 file changed, 8 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
> > > index fc31796..c4e5e34 100644
> > > --- a/lib/librte_vhost/vhost.h
> > > +++ b/lib/librte_vhost/vhost.h
> > > @@ -633,16 +633,20 @@ vhost_vring_call_split(struct virtio_net *dev,
> > struct vhost_virtqueue *vq)
> > >  	if (dev->features & (1ULL << VIRTIO_RING_F_EVENT_IDX)) {
> > >  		uint16_t old = vq->signalled_used;
> > >  		uint16_t new = vq->last_used_idx;
> > > +		bool signalled_used_valid = vq->signalled_used_valid;
> > > +
> > > +		vq->signalled_used = new;
> > > +		vq->signalled_used_valid = true;
> > >
> > >  		VHOST_LOG_DEBUG(VHOST_DATA, "%s:
> > used_event_idx=%d, old=%d, new=%d\n",
> > >  			__func__,
> > >  			vhost_used_event(vq),
> > >  			old, new);
> > > -		if (vhost_need_event(vhost_used_event(vq), new, old)
> > > -			&& (vq->callfd >= 0)) {
> > > -			vq->signalled_used = vq->last_used_idx;
> > > +
> > > +		if ((vhost_need_event(vhost_used_event(vq), new, old) &&
> > > +					(vq->callfd >= 0)) ||
> > > +				unlikely(!signalled_used_valid))
> > >  			eventfd_write(vq->callfd, (eventfd_t) 1);
> > > -		}
> > >  	} else {
> > >  		/* Kick the guest if necessary. */
> > >  		if (!(vq->avail->flags & VRING_AVAIL_F_NO_INTERRUPT)
> > > --
> > > 2.7.4
> > >