[dpdk-dev] [PATCH v3 4/5] vhost: batch update used ring

[Zhihong Wang <zhihong.wang@intel.com>]

This patch enables batch update of the used ring for better efficiency.

Signed-off-by: Zhihong Wang <zhihong.wang@intel.com>
---
 lib/librte_vhost/vhost-net.h  |  4 +++
 lib/librte_vhost/vhost_rxtx.c | 68 +++++++++++++++++++++++++++++++++----------
 lib/librte_vhost/virtio-net.c | 15 ++++++++--
 3 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/lib/librte_vhost/vhost-net.h b/lib/librte_vhost/vhost-net.h
index 51fdf3d..a15182c 100644
--- a/lib/librte_vhost/vhost-net.h
+++ b/lib/librte_vhost/vhost-net.h
@@ -85,6 +85,10 @@ struct vhost_virtqueue {
 
 	/* Physical address of used ring, for logging */
 	uint64_t		log_guest_addr;
+
+	/* Shadow used ring for performance */
+	struct vring_used_elem	*shadow_used_ring;
+	uint32_t		shadow_used_idx;
 } __rte_cache_aligned;
 
 /* Old kernels have no such macro defined */
diff --git a/lib/librte_vhost/vhost_rxtx.c b/lib/librte_vhost/vhost_rxtx.c
index 7523b2d..c4abaf1 100644
--- a/lib/librte_vhost/vhost_rxtx.c
+++ b/lib/librte_vhost/vhost_rxtx.c
@@ -155,7 +155,6 @@ enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
 	uint32_t mbuf_avail = 0;
 	uint32_t copy_len = 0;
 	uint32_t extra_buffers = 0;
-	uint32_t used_idx_round = 0;
 
 	/* start with the first mbuf of the packet */
 	mbuf_len = rte_pktmbuf_data_len(mbuf);
@@ -203,17 +202,11 @@ enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
 					goto rollback;
 			} else if (is_mrg_rxbuf) {
 				/* start with the next desc chain */
-				used_idx_round = vq->last_used_idx
-					& (vq->size - 1);
-				vq->used->ring[used_idx_round].id =
+				vq->shadow_used_ring[vq->shadow_used_idx].id =
 					desc_chain_head;
-				vq->used->ring[used_idx_round].len =
+				vq->shadow_used_ring[vq->shadow_used_idx].len =
 					desc_chain_len;
-				vhost_log_used_vring(dev, vq,
-					offsetof(struct vring_used,
-						ring[used_idx_round]),
-					sizeof(vq->used->ring[
-						used_idx_round]));
+				vq->shadow_used_idx++;
 				vq->last_used_idx++;
 				extra_buffers++;
 				virtio_hdr->num_buffers++;
@@ -248,12 +241,9 @@ enqueue_packet(struct virtio_net *dev, struct vhost_virtqueue *vq,
 		desc_chain_len += copy_len;
 	}
 
-	used_idx_round = vq->last_used_idx & (vq->size - 1);
-	vq->used->ring[used_idx_round].id = desc_chain_head;
-	vq->used->ring[used_idx_round].len = desc_chain_len;
-	vhost_log_used_vring(dev, vq,
-		offsetof(struct vring_used, ring[used_idx_round]),
-		sizeof(vq->used->ring[used_idx_round]));
+	vq->shadow_used_ring[vq->shadow_used_idx].id = desc_chain_head;
+	vq->shadow_used_ring[vq->shadow_used_idx].len = desc_chain_len;
+	vq->shadow_used_idx++;
 	vq->last_used_idx++;
 
 	return 0;
@@ -268,6 +258,45 @@ error:
 }
 
 static inline void __attribute__((always_inline))
+update_used_ring(struct virtio_net *dev, struct vhost_virtqueue *vq,
+		uint32_t used_idx_start)
+{
+	if (used_idx_start + vq->shadow_used_idx < vq->size) {
+		rte_memcpy(&vq->used->ring[used_idx_start],
+				&vq->shadow_used_ring[0],
+				vq->shadow_used_idx *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[used_idx_start]),
+				vq->shadow_used_idx *
+				sizeof(struct vring_used_elem));
+	} else {
+		uint32_t part_1 = vq->size - used_idx_start;
+		uint32_t part_2 = vq->shadow_used_idx - part_1;
+
+		rte_memcpy(&vq->used->ring[used_idx_start],
+				&vq->shadow_used_ring[0],
+				part_1 *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[used_idx_start]),
+				part_1 *
+				sizeof(struct vring_used_elem));
+		rte_memcpy(&vq->used->ring[0],
+				&vq->shadow_used_ring[part_1],
+				part_2 *
+				sizeof(struct vring_used_elem));
+		vhost_log_used_vring(dev, vq,
+				offsetof(struct vring_used,
+					ring[0]),
+				part_2 *
+				sizeof(struct vring_used_elem));
+	}
+}
+
+static inline void __attribute__((always_inline))
 notify_guest(struct virtio_net *dev, struct vhost_virtqueue *vq)
 {
 	rte_smp_wmb();
@@ -286,6 +315,7 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 {
 	struct vhost_virtqueue *vq;
 	struct virtio_net *dev;
+	uint32_t used_idx_start = 0;
 	uint32_t pkt_idx = 0;
 	uint32_t pkt_left = 0;
 	uint32_t pkt_sent = 0;
@@ -315,6 +345,8 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 	/* start enqueuing packets 1 by 1 */
 	pkt_idx = 0;
 	pkt_left = count;
+	vq->shadow_used_idx = 0;
+	used_idx_start = vq->last_used_idx & (vq->size - 1);
 	avail_idx = *((volatile uint16_t *)&vq->avail->idx);
 	while (1) {
 		if (loop_check(vq, avail_idx, pkt_left))
@@ -329,6 +361,10 @@ rte_vhost_enqueue_burst(int vid, uint16_t queue_id,
 		pkt_left--;
 	}
 
+	/* batch update used ring for better performance */
+	if (likely(vq->shadow_used_idx > 0))
+		update_used_ring(dev, vq, used_idx_start);
+
 	/* update used idx and kick the guest if necessary */
 	if (pkt_sent)
 		notify_guest(dev, vq);
diff --git a/lib/librte_vhost/virtio-net.c b/lib/librte_vhost/virtio-net.c
index 1785695..87d09fa 100644
--- a/lib/librte_vhost/virtio-net.c
+++ b/lib/librte_vhost/virtio-net.c
@@ -152,10 +152,14 @@ cleanup_device(struct virtio_net *dev, int destroy)
 static void
 free_device(struct virtio_net *dev)
 {
+	struct vhost_virtqueue *vq;
 	uint32_t i;
 
-	for (i = 0; i < dev->virt_qp_nb; i++)
-		rte_free(dev->virtqueue[i * VIRTIO_QNUM]);
+	for (i = 0; i < dev->virt_qp_nb; i++) {
+		vq = dev->virtqueue[i * VIRTIO_QNUM];
+		rte_free(vq->shadow_used_ring);
+		rte_free(vq);
+	}
 
 	rte_free(dev);
 }
@@ -418,13 +422,18 @@ int
 vhost_set_vring_num(int vid, struct vhost_vring_state *state)
 {
 	struct virtio_net *dev;
+	struct vhost_virtqueue *vq;
 
 	dev = get_device(vid);
 	if (dev == NULL)
 		return -1;
 
 	/* State->index refers to the queue index. The txq is 1, rxq is 0. */
-	dev->virtqueue[state->index]->size = state->num;
+	vq = dev->virtqueue[state->index];
+	vq->size = state->num;
+	vq->shadow_used_ring = rte_malloc("",
+			vq->size * sizeof(struct vring_used_elem),
+			RTE_CACHE_LINE_SIZE);
 
 	return 0;
 }
-- 
2.7.4