[PATCH v3 2/4] vhost: make the guest_notifications statistic counter atomic

[Eelco Chaudron <echaudro@redhat.com>]

Making the guest_notifications statistic counter atomic, allows
it to be safely incremented while holding the read access_lock.

Signed-off-by: Eelco Chaudron <echaudro@redhat.com>
---
 lib/vhost/vhost.c |    8 ++++++++
 lib/vhost/vhost.h |    9 ++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/lib/vhost/vhost.c b/lib/vhost/vhost.c
index 74bdbfd810..8ff6434c93 100644
--- a/lib/vhost/vhost.c
+++ b/lib/vhost/vhost.c
@@ -2086,6 +2086,10 @@ rte_vhost_vring_stats_get(int vid, uint16_t queue_id,
 
 	rte_rwlock_write_lock(&vq->access_lock);
 	for (i = 0; i < VHOST_NB_VQ_STATS; i++) {
+		/*
+		 * No need to the read atomic counters as such, due to the
+		 * above write access_lock preventing them to be updated.
+		 */
 		stats[i].value =
 			*(uint64_t *)(((char *)vq) + vhost_vq_stat_strings[i].offset);
 		stats[i].id = i;
@@ -2112,6 +2116,10 @@ int rte_vhost_vring_stats_reset(int vid, uint16_t queue_id)
 	vq = dev->virtqueue[queue_id];
 
 	rte_rwlock_write_lock(&vq->access_lock);
+	/*
+	 * No need to the reset atomic counters as such, due to the
+	 * above write access_lock preventing them to be updated.
+	 */
 	memset(&vq->stats, 0, sizeof(vq->stats));
 	rte_rwlock_write_unlock(&vq->access_lock);
 
diff --git a/lib/vhost/vhost.h b/lib/vhost/vhost.h
index 5c939ef06f..37609c7c8d 100644
--- a/lib/vhost/vhost.h
+++ b/lib/vhost/vhost.h
@@ -135,11 +135,12 @@ struct virtqueue_stats {
 	uint64_t broadcast;
 	/* Size bins in array as RFC 2819, undersized [0], 64 [1], etc */
 	uint64_t size_bins[8];
-	uint64_t guest_notifications;
 	uint64_t iotlb_hits;
 	uint64_t iotlb_misses;
 	uint64_t inflight_submitted;
 	uint64_t inflight_completed;
+	/* Counters below are atomic, and should be incremented as such. */
+	uint64_t guest_notifications;
 };
 
 /**
@@ -907,7 +908,8 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 				unlikely(!signalled_used_valid)) {
 			eventfd_write(vq->callfd, (eventfd_t) 1);
 			if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-				vq->stats.guest_notifications++;
+				__atomic_fetch_add(&vq->stats.guest_notifications,
+					1, __ATOMIC_RELAXED);
 			if (dev->notify_ops->guest_notified)
 				dev->notify_ops->guest_notified(dev->vid);
 		}
@@ -917,7 +919,8 @@ vhost_vring_call_split(struct virtio_net *dev, struct vhost_virtqueue *vq)
 				&& (vq->callfd >= 0)) {
 			eventfd_write(vq->callfd, (eventfd_t)1);
 			if (dev->flags & VIRTIO_DEV_STATS_ENABLED)
-				vq->stats.guest_notifications++;
+				__atomic_fetch_add(&vq->stats.guest_notifications,
+					1, __ATOMIC_RELAXED);
 			if (dev->notify_ops->guest_notified)
 				dev->notify_ops->guest_notified(dev->vid);
 		}