[dpdk-dev] [PATCH v2] vhost: fix interrupt suppression for the split ring

[Jiayu Hu <jiayu.hu@intel.com>]

The VIRTIO_RING_F_EVENT_IDX feature of split ring might
be broken, as the value of signalled_used is invalid
after live migration, start up and virtio driver reload.
This patch fixes it by using signalled_used_valid.

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@dpdk.org

Signed-off-by: Jiayu Hu <jiayu.hu@intel.com>
---
change in v2:
- fix virtio-net driver reload

 lib/librte_vhost/vhost.h      | 12 ++++++++----
 lib/librte_vhost/vhost_user.c |  2 ++
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/librte_vhost/vhost.h b/lib/librte_vhost/vhost.h
index f008ec4..e9138df 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)
diff --git a/lib/librte_vhost/vhost_user.c b/lib/librte_vhost/vhost_user.c
index 36c0c67..01a8d80 100644
--- a/lib/librte_vhost/vhost_user.c
+++ b/lib/librte_vhost/vhost_user.c
@@ -1298,6 +1298,8 @@ vhost_user_get_vring_base(struct virtio_net **pdev,
 
 	vq->callfd = VIRTIO_UNINITIALIZED_EVENTFD;
 
+	vq->signalled_used_valid = false;
+
 	if (dev->dequeue_zero_copy)
 		free_zmbufs(vq);
 	if (vq_is_packed(dev)) {
-- 
2.7.4