vhost: flush enqueue updates by cacheline

Buffer vhost packed ring enqueue updates, flush ring descs if buffered
content filled up one cacheline. Thus virtio can receive packets at a
faster frequency.

Signed-off-by: Marvin Liu <yong.liu@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

lib/librte_vhost/vhost.h

@@ -174,6 +174,8 @@ struct vhost_virtqueue {
 		struct vring_used_elem_packed *shadow_used_packed;
 	};
 	uint16_t                shadow_used_idx;
+	/* Record packed ring enqueue latest desc cache aligned index */
+	uint16_t		shadow_aligned_idx;
 	struct vhost_vring_addr ring_addrs;
 
 	struct batch_copy_elem	*batch_copy_elems;

lib/librte_vhost/virtio_net.c

@@ -91,6 +91,69 @@ update_shadow_used_ring_split(struct vhost_virtqueue *vq,
 	vq->shadow_used_split[i].len = len;
 }
 
+static __rte_always_inline void
+vhost_flush_enqueue_shadow_packed(struct virtio_net *dev,
+				  struct vhost_virtqueue *vq)
+{
+	int i;
+	uint16_t used_idx = vq->last_used_idx;
+	uint16_t head_idx = vq->last_used_idx;
+	uint16_t head_flags = 0;
+
+	/* Split loop in two to save memory barriers */
+	for (i = 0; i < vq->shadow_used_idx; i++) {
+		vq->desc_packed[used_idx].id = vq->shadow_used_packed[i].id;
+		vq->desc_packed[used_idx].len = vq->shadow_used_packed[i].len;
+
+		used_idx += vq->shadow_used_packed[i].count;
+		if (used_idx >= vq->size)
+			used_idx -= vq->size;
+	}
+
+	rte_smp_wmb();
+
+	for (i = 0; i < vq->shadow_used_idx; i++) {
+		uint16_t flags;
+
+		if (vq->shadow_used_packed[i].len)
+			flags = VRING_DESC_F_WRITE;
+		else
+			flags = 0;
+
+		if (vq->used_wrap_counter) {
+			flags |= VRING_DESC_F_USED;
+			flags |= VRING_DESC_F_AVAIL;
+		} else {
+			flags &= ~VRING_DESC_F_USED;
+			flags &= ~VRING_DESC_F_AVAIL;
+		}
+
+		if (i > 0) {
+			vq->desc_packed[vq->last_used_idx].flags = flags;
+
+			vhost_log_cache_used_vring(dev, vq,
+					vq->last_used_idx *
+					sizeof(struct vring_packed_desc),
+					sizeof(struct vring_packed_desc));
+		} else {
+			head_idx = vq->last_used_idx;
+			head_flags = flags;
+		}
+
+		vq_inc_last_used_packed(vq, vq->shadow_used_packed[i].count);
+	}
+
+	vq->desc_packed[head_idx].flags = head_flags;
+
+	vhost_log_cache_used_vring(dev, vq,
+				head_idx *
+				sizeof(struct vring_packed_desc),
+				sizeof(struct vring_packed_desc));
+
+	vq->shadow_used_idx = 0;
+	vhost_log_cache_sync(dev, vq);
+}
+
 static __rte_always_inline void
 flush_shadow_used_ring_packed(struct virtio_net *dev,
 			struct vhost_virtqueue *vq)
@@ -194,6 +257,33 @@ do_data_copy_dequeue(struct vhost_virtqueue *vq)
 	vq->batch_copy_nb_elems = 0;
 }
 
+static __rte_always_inline void
+vhost_shadow_enqueue_single_packed(struct virtio_net *dev,
+				   struct vhost_virtqueue *vq,
+				   uint32_t len[],
+				   uint16_t id[],
+				   uint16_t count[],
+				   uint16_t num_buffers)
+{
+	uint16_t i;
+	for (i = 0; i < num_buffers; i++) {
+		/* enqueue shadow flush action aligned with batch num */
+		if (!vq->shadow_used_idx)
+			vq->shadow_aligned_idx = vq->last_used_idx &
+				PACKED_BATCH_MASK;
+		vq->shadow_used_packed[vq->shadow_used_idx].id  = id[i];
+		vq->shadow_used_packed[vq->shadow_used_idx].len = len[i];
+		vq->shadow_used_packed[vq->shadow_used_idx].count = count[i];
+		vq->shadow_aligned_idx += count[i];
+		vq->shadow_used_idx++;
+	}
+
+	if (vq->shadow_aligned_idx >= PACKED_BATCH_SIZE) {
+		do_data_copy_enqueue(dev, vq);
+		vhost_flush_enqueue_shadow_packed(dev, vq);
+	}
+}
+
 /* avoid write operation when necessary, to lessen cache issues */
 #define ASSIGN_UNLESS_EQUAL(var, val) do {	\
 	if ((var) != (val))			\
@@ -785,6 +875,9 @@ vhost_enqueue_single_packed(struct virtio_net *dev,
 	uint16_t desc_count;
 	uint32_t size = pkt->pkt_len + dev->vhost_hlen;
 	uint16_t num_buffers = 0;
+	uint32_t buffer_len[vq->size];
+	uint16_t buffer_buf_id[vq->size];
+	uint16_t buffer_desc_count[vq->size];
 
 	if (rxvq_is_mergeable(dev))
 		max_tries = vq->size - 1;
@@ -810,6 +903,9 @@ vhost_enqueue_single_packed(struct virtio_net *dev,
 		len = RTE_MIN(len, size);
 		size -= len;
 
+		buffer_len[num_buffers] = len;
+		buffer_buf_id[num_buffers] = buf_id;
+		buffer_desc_count[num_buffers] = desc_count;
 		num_buffers += 1;
 
 		*nr_descs += desc_count;
@@ -821,6 +917,9 @@ vhost_enqueue_single_packed(struct virtio_net *dev,
 	if (copy_mbuf_to_desc(dev, vq, pkt, buf_vec, nr_vec, num_buffers) < 0)
 		return -1;
 
+	vhost_shadow_enqueue_single_packed(dev, vq, buffer_len, buffer_buf_id,
+					   buffer_desc_count, num_buffers);
+
 	return 0;
 }
 
@@ -1017,7 +1116,7 @@ virtio_dev_rx_packed(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	do_data_copy_enqueue(dev, vq);
 
 	if (likely(vq->shadow_used_idx)) {
-		flush_shadow_used_ring_packed(dev, vq);
+		vhost_flush_enqueue_shadow_packed(dev, vq);
 		vhost_vring_call_packed(dev, vq);
 	}